Health Library

Article

Pregnancy Screening Tests

Pregnancy is the period of time when a fetus develops inside a woman’s uterus and ends with the birth of the infant. There are a variety of clinical laboratory tests related to pregnancy, from the time pregnancy is first considered through the initial days of the newborn’s life. Some of these tests are performed on most women at specified times throughout the pregnancy, others are ordered as needed to detect and address conditions or problems that arise during pregnancy. Some are offered to women who have increased risks because of their age or lifestyle, while others are selectively chosen based on the woman’s and her partner’s personal and family history.

The purpose of these tests is to diagnose existing problems that may affect the mother’s or baby’s health, identify and address problems as they arise, and to assess the risk of a baby having a chromosomal or genetic abnormality.

Most of the routine tests are associated with infections or conditions that should be resolved prior to a woman getting pregnant or, if she is already pregnant, should be resolved and/or monitored during her pregnancy.

The following pages contain information on many of these routine and some of the less routine tests. There may be, however, other tests that your doctor will recommend based on your personal medical history.

Pre-Conception (Pre-Pregnancy)

When a couple is considering having a child, they should consult with their doctor(s). Based on their family and medical histories, the health care professional(s) may recommend some or all of the following key routine laboratory tests:

• Immunity to Rubella (German Measles)

• HIV

• Gonorrhea, chlamydia, and syphilis

• Blood Type and Antibody screen

• Hepatitis B screening

• Hemoglobin

• Pap test

Other less routine testing:

• Varicella zoster viral testing for immunity to chicken pox

• TORCH panel if herpes, CMV, or toxoplasmosis is suspected

• Bacterial vaginosis

Testing that may be offered to both the woman and her partner to evaluate the risk of inherited diseases:

• Genetic testing for inherited diseases

• Genetic hemoglobin disorders

• Cystic fibrosis

Immunity to Rubella (German Measles)

Rubella is caused by a virus that is passed from person-to-person by coughs or sneezes. Any contact with the nasal or throat secretions of an infected person can spread the virus. Women who have either had a Rubella infection or have received the vaccination will have an antibody in their blood that will usually prevent them from getting the infection a second time. This antibody also protects the unborn baby against the virus; this protection is called immunity.

Rubella infections during childhood usually cause mild symptoms. However, if a woman becomes infected with Rubella during the first three months of her pregnancy and does not have immunity to the virus, the baby is at risk of having serious birth defects or dying.

All women considering a first time pregnancy, or those who are pregnant for the first time, should be tested to see if they have this immunity. A blood specimen is tested to see if a sufficient amount of antibody is present in the blood to protect the mother and the baby. If a woman does not have enough antibodies and is not currently pregnant, she may be given a Rubella vaccination. She should then wait about 2 to 3 months before becoming pregnant.

The Rubella vaccine is a weakened form of a live virus and should not be given to a woman who is currently pregnant. If a pregnant woman does not have sufficient antibody to protect her and her baby, she will be advised by her doctor to avoid contact with anyone who has symptoms of rubella throughout the rest of her pregnancy. She should consult with her doctor about the best time to get vaccinated after her baby is born and follow through with getting a Rubella vaccination so that her next baby will be protected.

Related Tests

Rubella, TORCH

HIV

HIV is the virus that causes AIDS (Acquired Immunodeficiency Syndrome). At least 90-95% of individuals who are infected with the HIV virus will, within three months of exposure, develop enough antibodies to have a positive HIV test; over 99% of HIV infected individuals will have a positive test within six months. If a pregnant woman is infected with the HIV virus, it can be passed to and infect her baby.

The HIV test detects antibodies to HIV in the blood. Although a positive HIV test could mean a woman is infected with HIV, the test may also be positive for other reasons. The laboratory will automatically perform additional testing to determine conclusively if there is an HIV infection. If a woman’s confirmatory tests indicate an HIV infection, she will want to consult with her doctor about the risks of infecting a baby and the affects of the pregnancy on her health prior to becoming pregnant. While a pregnant woman with an HIV infection does have the virus present in her body and can infect others, treatments given during pregnancy can help minimize the chance of passing the HIV infection to her baby.

A negative test for the antibody to HIV may mean that there is no infection or that a sufficient amount of the antibody has not yet been produced to be detected. If a woman participates in high risk activities that may transmit HIV, such as unprotected sexual contact or intravenous drug use, it is recommended that she be retested one or more additional times during the pregnancy.

Related Test

HIV antibody test

Gonorrhea, Chlamydia, and Syphilis

These are three common sexually transmitted diseases (STDs). These diseases are caused by bacterial infections and can lead to a miscarriage or can infect the baby prior to or during delivery.

Women may be tested for these STDs prior to pregnancy or during their first prenatal visit. If a woman engages in high risk activities during her pregnancy, such as unprotected sexual contact, then her doctor may retest for STDs.

The Syphilis test is a blood test that detects an antibody produced by the body in response to the infection. It does not distinguish between a current or past infection and, if it is positive, confirmatory testing will be required. A negative test result usually means the woman is not currently infected; however, it is possible that an infection is too new to detect.

Chlamydia and gonorrhea tests detect the actual bacteria in a cervical (or other body fluid) sample. If they are positive, then the patient has a current STD infection that requires treatment.

Related Tests

Tests: Gonorrhea, Chlamydia, Syphilis

Blood Type and Antibody Screen

Blood types are either A, B, AB, or O, and Rh positive or negative. Both the mother and baby may experience problems if their blood types are different, or if the mother has antibodies (antiglobulins) that will react with antigens (proteins or factors) on the baby’s red blood cells.

The best known example is when an Rh-negative woman is pregnant with an Rh-positive baby. The woman’s immune system can develop an antibody that attaches to the Rh-positive antigens on her baby’s red blood cells and target them for destruction. Although it is unusual for her first Rh-positive baby to become ill, the antibodies produced during that first pregnancy will affect any future Rh-positive babies. To greatly reduce the likelihood that an Rh-negative mother will develop this antibody, she may be given a routine injection of Rh immune globulin (RhoGam) at approximately 28 weeks gestation. Additional injections may be necessary during the pregnancy if she has an amniocentesis, chorionic villi sampling, or an abdominal injury, and after delivery if the baby is Rh-positive. Before each injection is given, an antibody screen (indirect antiglobulin test) is performed to make sure that the woman has not already created Rh antibodies.

In addition to Rh-negative women who have had an Rh-positive baby, any woman who has had a blood transfusion or had prior pregnancies may produce an antibody to blood factors other than Rh that can potentially harm an unborn baby. An antibody screen during the first trimester is ordered to determine if potentially harmful antibodies are already present in the mother’s blood. If a harmful antibody is detected, the baby’s father should be tested, if possible, to see if his blood has antigens that react with the mother’s antibody. If it does react, then the baby’s may also. If there is a possibility that the antibody could react with the baby’s, then it is advisable for the health care provider to monitor the mother’s antibody level and the progress of the baby for the duration of the pregnancy. Signs that the fetus is becoming ill may necessitate that it receive treatment before birth (such as an intrauterine transfusion) or require an early delivery.

Limitations of the antibody screen:

An antibody may be present but in an amount too low to be detected.

The baby’s blood may react with the antibody even if the test is negative.

Related Test

Indirect antiglobulin test

Hepatitis B Screening

Infection with the Hepatitis B virus causes an inflammation of the liver. People with acute Hepatitis B may have symptoms such as fatigue, nausea, and jaundice. Most people will get better without any intervention, but about 1-3% become carriers - chronically infected and able to continue to infect others. Some of those chronically infected will have progressive liver damage that can lead to liver cancer and death.

The Hepatitis B screening test is called a Hepatitis B Surface Antigen. It detects a protein produced by the virus and can detect a Hepatitis B infection even before it is causing symptoms. If a woman who is considering getting pregnant tests positive for Hepatitis B, she should talk to her doctor about how long she should wait for the infection to resolve before becoming pregnant.

It is important to detect active Hepatitis B infections in pregnant women because newborns are especially vulnerable to developing chronic infection; up to 90% of those who become infected with Hepatitis B will become carriers. If a hepatitis infection is detected in a pregnant woman, she can be monitored and the baby can receive treatment at birth to minimize the risk of its developing Hepatitis B.

A negative test for the virus means either that there is no current infection or that there is not yet a sufficient amount of the antigen to be detected. If a woman participates in high risk activities that may transmit the Hepatitis B virus, such as unprotected sexual contact or intravenous drug use, it is recommended that she be retested again later in the pregnancy.

Related Test

Hepatitis B

Hemoglobin

Hemoglobin is the protein in red blood cells (RBCs) that gives blood its red color. It binds to oxygen in your lungs, transports it throughout the body, and releases it to the cells and tissues. During pregnancy, a woman’s hemoglobin must transport enough oxygen to meet both her and her baby’s needs. If a woman has insufficient hemoglobin, she is said to be anemic. Many pregnant women will experience some degree of anemia. Anemia can be caused by decreased RBC production, increased RBC destruction, or by increased RBC (blood) loss.

Mild anemia can make you feel tired and weak while severe anemia may cause you to lose consciousness and in extreme cases can cause death. Anemia in a pregnant mother can cause a fetus to receive too little oxygen to support normal development. To prevent these problems, the hemoglobin level of a woman’s blood will be checked prior to pregnancy, at the beginning of pregnancy, and one or more times during pregnancy. The first baseline concentrations will be compared to later values to look for changes that could indicate increasing anemia.

Often a hemoglobin will be run as part of a Complete Blood Count (CBC). The CBC also measures the actual number of RBCs, the number and type of white blood cells (WBCs), the number of platelets (cell fragments involved in blood clotting), and the hematocrit (the amount of solids versus liquids in the blood).

Iron deficiency is the most common cause of anemia, but vitamin deficiency, kidney disease, inherited hemoglobin disorders, and other illnesses can also cause anemia. It is also possible to have a higher than normal hemoglobin level. This is usually caused by dehydration, but may also result from a variety of diseases. Treatment for the unexpected hemoglobin level will depend upon the medical cause of the problem.

Related Tests

Hemoglobin, CBC, Hematocrit

Pap Test

A Pap test is performed to screen the cervix (opening to the uterus) for cancer, pre-cancerous changes, inflammation, and some sexually transmitted diseases. It is ordered on a woman at intervals that are recommended by her doctor. In most cases, if a woman has had a recent normal Pap test, she will not require another test when she becomes pregnant. If it has been several months to a year or more since the last Pap test, or if there are any questions about the status of the cervix, the doctor may perform another Pap test at the beginning of the pregnancy.

Early detection of abnormal cervical cells and infections and early treatment, if necessary, offer the best chance to prevent any problems from progressing and potentially affecting the health of the baby and the success of the pregnancy.

Related Test

Pap smear

Varicella Zoster Virus

Varicella zoster virus (VZV) causes the illness known as chicken pox. Although most (85-90%) pregnant women have already been exposed to the virus and therefore are immune, some may not have previously had the infection. Since the virus can cause birth defects or illness in the baby (depending on when during the pregnancy an infection occurs), testing is available pre-conception or in early pregnancy to determine if the woman has antibodies to VZV. If she doesn’t and is therefore not immune, a vaccine can be given before the woman gets pregnant; if she is already pregnant and may have been exposed to the virus, treatment is available that can prevent or weaken the severity of the illness.

TORCH Panel

The TORCH panel is used to screen for four infectious diseases that can cause birth defects in a baby if the mother contracts them during the pregnancy. The tests that make up the panel are for rubella, toxoplasmosis, cytomegalovirus (CMV), and herpes simplex virus (HSV). The rubella test is more commonly ordered individually, either before or in early pregnancy. The complete TORCH panel is less commonly ordered since more specific and sensitive tests to detect these infections are available.

Toxoplasmosis is a disease caused by a parasite found in undercooked meat from an infected animal, exposure to cat feces (where the parasite egg is frequently found), or from soil (such as gardening soil) contaminated by the parasite. A woman who becomes infected during pregnancy may develop swollen lymph nodes, fatigue and flu-like symptoms. Fetuses infected during early gestation are more adversely affected than if exposed later in the pregnancy. Newborns infected with toxoplasmosis may appear normal at birth, but, as the baby becomes older, may develop vision or hearing loss, display learning disabilities, mental retardation, or seizures. Severe cases may result in death.

Diagnosis of this condition can be difficult. A test for toxoplasmosis detects the antibodies that are produced after exposure to the parasite; however, a positive result does not distinguish between current or prior parasite infections. If a woman tests positive prior to conception, her test should be repeated in a few weeks to see if the amount of antibody is increasing, indicating a current infection needing treatment. If the amount remains the same, then the antibodies are most likely due to a previous infection. Women who test positive should consult with their doctor on the right amount of time to wait before becoming pregnant. A negative toxoplasmosis test means either there is not a current infection or that the amount of antibody produced is not yet sufficient to be detected.

If the woman is in frequent contact with a cat, but does not yet have a positive test for toxoplasmosis, the health care provider may recommend that she either avoid or use gloves and care when handling cat wastes and be tested for antibodies one or more additional times during the pregnancy. If a woman becomes infected during her pregnancy, she usually will be treated with a medication to help decrease the likelihood that the infection is passed on to her fetus.

Cytomegalovirus is a viral infection that the mother may pass to the fetus during the birth process but that can also infect newborns through breast milk. Infected infants may have severe problems, such as hearing loss, mental retardation, pneumonia, hepatitis, or blood disorders.

Herpes simplex virus is a common viral infection that manifests as sores on either the lips or genitals. Newborns who contract the virus usually do so during travel through the birth canal of a woman who has a genital infection with HSV. The virus may spread throughout the newborn’s body, attacking vital organs. Treatment with specific antiviral medication should begin as soon as possible in the infected newborn. Even if treated, surviving babies may have permanent damage to the central nervous system.

Related Tests

Rubella, CMV, Herpes Simplex Virus

Bacterial Vaginosis Screen

Bacterial vaginosis, an overgrowth of a normal flora (bacteria) in the vagina that causes a vaginal discharge, is relatively common in both pregnant and non-pregnant women. If a woman is having preconception testing done, her doctor may do a “wet prep” (wet mount) in the doctor’s office by placing a sample of vaginal secretions on a slide with saline or potassium hydroxide and looking at it under the microscope for bacteria. A doctor may also order a genital culture to check the vaginal sample for the presence of other types of bacteria that may be causing an infection. Doctors do not order this test routinely on pregnant women, but will order it as needed for those who have symptoms such as a vaginal discharge or itching.

Symptoms of bacterial vaginosis may include:

• vaginal discharge that is not clear in appearance

• presence of a specific type of cell when examined microscopically

• amine (fishy) odor when the discharge is tested with a chemical

• a decrease in acidity of the vagina

If the patient has three of these four symptoms, she is diagnosed with bacterial vaginosis (bacteria in the vagina). It is usually cured with a seven-day treatment of a prescribed antibiotic. Untreated bacterial vaginosis during pregnancy can result in amniotic fluid infection, premature rupture of the membranes, premature delivery, low birth weight of the baby, and possibly pelvic inflammatory disease in the mother.

Genetic Testing for Inherited Diseases

There are hundreds of diseases that are related to changes in our genetic code, but most of them are extremely rare. Mutations or alterations in specific genes may prevent the genes from creating vital proteins or cause alterations in the proteins that they produced. These changes can affect the way that the body functions and cause specific diseases. Some of the disease-related gene mutations are recessive before they cause dysfunction, while others are dominant (a single altered gene copy can cause disease). Some are X- or sex-linked, associated with the X or Y chromosome that determines our gender, and are found only in males or females. Some mutations have arisen and been passed down in specific families and some are more prevalent in individuals of certain ethnic descent.

Genetic testing is a personal choice. Testing for some of the more common genetic diseases may be performed on both a woman and her partner prior to a pregnancy. Couples should talk to a genetic counselor about their ethnicity and family background to determine which tests are the most appropriate and to help them make an informed decision.

Individuals of Ashkinazi (East European) Jewish descent, for example, are at increased risk for inheriting Tay-Sachs, Gaucher, Canavan disease, and Familial Dysautonomia. These genetic diseases can occur when both parents have an abnormal gene that can cause the disease in the child. In both Tay-Sachs and Canavan diseases, there is a buildup of a substance in the child’s brain that prevents normal development. There is no known cure for either disease. Children with Tay-Sachs rarely live past five years of age; children with Canavan disease may live to early adolescence. There are three types of Gaucher disease, each causing too much fatty substance to be stored in the bone marrow, spleen and liver. Although one type of Gaucher disease is fatal, the most common type is not. Treatments are available for individuals with Gaucher disease. Famial Dysautonomia is caused by incomplete development of nerve fibers in the autonomic and sensory nervous systems. There are a variety of symptoms (and their severity), the most noticeable of which is the lack of tears during crying.

Genetic Hemoglobin Disorders: Hemoglobinopathies and Thalessemias

Hemoglobin is a protein that binds and releases oxygen. Found in all red blood cells (RBCs), hemoglobin transports oxygen throughout the body and releases it to the cells and tissues. Each person inherits genes from both of their parents that make hemoglobin. Some individuals inherit abnormal genes that can cause hemoglobin disorders. In diseases called thalassemias, the hemoglobin genes make normal hemoglobin but not enough to supply the body with sufficient oxygen. Inheriting one or more thalassemia genes from one or both parents can cause mild to severe anemia and the production of smaller and paler RBCs.

In diseases called hemoglobinopathies, the hemoglobin genes make abnormal hemoglobin that may not function like normal hemoglobin. It usually takes two abnormal genes, one from each parent, to cause disease. The best known example is Sickle Cell Disease, a serious hemoglobinopathy that causes anemia, susceptibility to infection, and organ damage in affected infants. Carriers of the sickle cell disease (those who have inherited only one sickle hemoglobin gene) do not get the disease but can pass their abnormal gene onto their children. If a carrier of the disease has a child with another carrier, their child is at risk of inheriting the sickle cell gene from each parent and having the disease.

If a patient or her partner has a strong family history of thalassemia or hemoglobinopathy or is of an ethnicity which has an increased prevalence of one of the diseases, she and her partner may want to talk to a genetic counselor about genetic testing before getting pregnant. For example, Sickle Cell Disease is most common in people of African heritage. Thalassemias are most common in people of Mediterranean, African, or Asian descent.

Related Tests

Sickle cell, Hemoglobin Variants

Cystic Fibrosis

Cystic fibrosis (CF) is a relatively common recessive genetic disorder that is caused by a mutation in a particular gene. If a person receives an altered gene from one parent and a normal gene from the other parent, he or she will be a CF carrier. Carriers do not have symptoms and are not ill, but they may pass their abnormal copy of the gene on to their children. About 1,000 different CF gene mutations have been identified, but only a few are common. Caucasians from Northern Europe and Ashkenazi Jews have the highest population carrier rates (about 1 in 20-25).

If both parents are CF carriers and pass the altered genes on to their child, then that child will have cystic fibrosis. Patients with CF have thick, sticky mucus in their lungs and pancreas. This can lead to frequent respiratory infections, obstructed pancreatic and liver ducts, and impaired protein digestion. The majority of males with CF are also infertile due to missing or underdeveloped vas deferens, the tubules that transport sperm from the testes. Most people with CF will develop respiratory and pancreatic symptoms very early, although symptom severity will vary from person to person, even in those with the exact same mutation.

Laboratories are now able to perform CF gene mutation testing to check for 25 or more common CF gene mutations. Couples who are planning to become pregnant may want to talk to their doctor and a genetic counselor about this test and other genetic testing. A genetic counselor will be able to provide additional information and help to make an educated decision about the risk of having a child born with Cystic Fibrosis. Those who have an identified CF gene mutation in their family should be tested specifically for that mutation.

Related Test

CF Gene Mutation

First Trimester (up to 12 weeks)

If a pre-conception medical checkup was not done, at the time of the first prenatal visit, the health care provider will order several or most of the routine tests described in the Pre-conception section and also talk about other tests. These additional tests will be used to further evaluate the health and future medical care needs of the mother. In addition to the tests listed in the Pre-conception section, the following tests may be ordered:

• Pregnancy test

• Urine screen for sugar and/or protein

• Urine culture and sensitivity

• Down syndrome screening

It is now possible during the early stages of pregnancy (10-13 weeks) to estimate the possibility of a mother having a Down’s-affected baby using biochemical tests, sometimes in combination with ultrasound measurements. These tests may also indicate the possibility of other chromosome disorders, such as Edward’s syndrome. This type of screening provides an opportunity to assess the possibility of these conditions being present without performing more invasive procedures such as chorionic villus sampling (see below) or amniocentesis. Only those women whose screening results indicate that they are in a higher risk group are currently counselled about having further tests.

Screening includes the measurement of blood levels of pregnancy associated plasma protein A (PAPP-A) and either free or total human chorionic gonadotrophin (hCG). In addition, an ultrasound scan, called nuchal translucency is done. This involves taking a measurement of the thickness of the skin and tissue at the back of the baby’s neck. The results from these tests will be combined and used to calculate the chance of the baby having Down’s syndrome or another chromosome abnormality.

The following test is not routinely performed but may be offered to and discussed with women who are at an increased risk of having a baby with chromosomal or genetic abnormalities.

• Chorionic villi sampling (CVS)

Pregnancy Test

If pregnancy is only suspected, or if the pregnancy test was not performed through the health care provider (such as an at-home urine pregnancy test), then a pregnancy test may be requested to confirm that a woman is pregnant.

Pregnancy tests all measure the same substance, human chorionic gonadotropin (hCG), a hormone that is produced by the placenta when a woman is pregnant. The amount of hCG produced during pregnancy doubles every two to three days and then levels off in the second or third month of pregnancy. Qualitative urine and blood pregnancy tests can detect hCG as early as several days to two weeks after conception.

Quantitative blood pregnancy testing measures the actual amount of hCG present. Each woman will produce the hormone at a slightly different rate, but women with normal pregnancies should have hCG concentrations that fall within established ranges for each week of gestation. Quantitative hCG tests may be repeated every couple of days if there is a problem with the pregnancy to look at changes in the concentration of hCG.

A level of hCG lower than expected may be due to incorrect calculation of gestational age or a problem in fetal development, which may lead to miscarriage. The test may be repeated or an ultrasound done to compare the size of the developing baby to the expected size for the duration of gestation. Patients with ectopic pregnancies (a pregnancy occurring in a location other than the uterus, such as the fallopian tubes) will have lower than expected values that will increase more slowly than expected. Patients who have failing pregnancies may have stagnant or dropping hCG levels.

Related Test

hCG

Urine Screen for Sugar and/or Protein

At each prenatal visit, the expectant mother will be asked to give a urine specimen that will be screened for the presence of sugar and/or protein.

Although a small amount of sugar normally may be present in urine, high levels may be a sign of gestational diabetes, a form of diabetes that develops during pregnancy. A positive urine test for sugar will usually be followed by a confirmatory blood test. Approximately four percent of women with no prior history of diabetes will develop gestational diabetes. Although it can occur at any time, most cases will develop during the later part of a woman’s pregnancy.

Gestational diabetes does not usually continue following delivery, but it does increase the risk of a woman developing type 2 diabetes later in life Â? about fifty percent of the women who have gestational diabetes will later develop type 2 diabetes. Women who have gestational diabetes with one pregnancy are more likely to also have it in any subsequent pregnancies. A blood glucose test for gestational diabetes is routinely performed during the second trimester.

A special diet, insulin, or both may be needed to adjust the glucose level down to normal. If the diabetes is not controlled, the mother may develop preeclampsia. Preeclampsia usually does not occur until the second half of pregnancy. The symptoms include high blood pressure (hypertension), swelling that doesn't go away, infections, and large amounts of protein in the urine. Maternal high glucose concentrations can also cause abnormal growth and development of the unborn baby. Complications of high uncontrolled blood sugar may require the baby to be delivered prematurely.

Although small amounts of protein are normally present in the urine, high levels may indicate infection of the bladder and kidneys.

Related Tests

Urinalysis, Glucose, Urine Protein

Urine Culture and Sensitivity

Urinary tract infections frequently cause symptoms that require pregnant women to seek treatment, but bacteria may also be present in the urine without causing noticeable symptoms. For this reason, many doctors routinely order urine cultures on their pregnant patients.

If left untreated, these bacteria may spread from the bladder to the kidneys. An infection in the kidneys can decrease their ability to function. If bacteria are found, antibiotics may be prescribed. After the antibiotic treatment has been completed, a new urine specimen may be needed to confirm that the bacteria are no longer present.

Limitations of urine cultures:

Improper cleaning of the area prior to collection of the urine specimen may result in a specimen that is contaminated with bacteria from the vagina or skin. These bacteria do not generally cause infections but may mask the presence of harmful bacteria.

Related Tests

Urine Culture, Urinalysis

Chorionic Villi Sampling (CVS)

Between the tenth and twelfth week, a Chorionic Villi Sampling (CVS) procedure can be performed to obtain cells from the placenta that have the same genetic make-up as the fetus. These cells are analyzed for chromosomal disorders, such as is seen in Down syndrome, and gene abnormalities that cause metabolic disorders, such as Tay-Sachs and Cystic Fibrosis.

Although available to anyone, the usual indications for this procedure are if:

• the pregnant woman is 35 years of age or older,

• there is a strong family history of a specific genetic disorder, or

• both parents possess a gene for an inherited disorder.

Risks associated with CVS:

There is a risk of miscarriage associated with the CVS procedure. An infection may develop.

Limitations of CVS:

Not all genetic disorders can be detected. For certain genetic tests, there is greater reliability of results when testing individuals whose ethnicity puts them at a higher risk (because there is a higher than normal prevalence of specific genetic disorders in that ethnic group).

Second Trimester (13 - 27 weeks)

The tests performed during the second trimester provide information to evaluate both actual and potential medical problems in the baby.

Routine tests:

• Urine screen for sugar and/or protein

• Glucose/Glucose Tolerance Test

Selective tests:

• Triple Marker or Quad marker screen

• Amniocentesis

Urine Screen for Sugar and/or Protein

At each prenatal visit during this trimester, a urine specimen will be tested for the presence of sugar and/or protein.

Of particular concern during the second and third trimesters is preeclampsia (sometimes called toxemia or pregnancy-induced hypertension), a disorder characterized by high blood pressure and large amounts of protein in the urine that occurs in approximately 8% of all pregnancies. Symptoms include swelling, sudden weight gain, headache, and vision changes. Risk factors include first pregnancy, carrying multiple babies, age (teenagers and women over 40), being African American, and having pre-existing diabetes, hypertension, or kidney disease. It can result in a decrease of air and food getting to the baby through the placenta, causing low birth weight or other complications. If caught early enough, however, through routine checking of blood pressure and urine protein levels, health problems for the mother and baby due to preeclampsia can be prevented.

Blood Glucose

During pregnancy, about four percent of women with no prior history of diabetes will develop gestational diabetes (increased glucose levels). Although it can occur at any time, most cases will develop during the later part of a woman’s pregnancy. If increased blood sugar levels in the mother are uncontrolled, they can cause the baby to increase in size and weight. They can also cause the baby to be born with very low glucose levels and to have breathing difficulties.

Most women will be checked for gestational diabetes between 24 and 28 weeks of pregnancy. At the beginning of the glucose screening test, the mother is asked to consume a drink containing a known amount of glucose and, an hour later, a blood specimen is collected. If the level of glucose is acceptable, then it is unlikely that she has gestational diabetes. If the level is moderately elevated, a longer, more conclusive glucose tolerance test (GTT) may be discussed. If the level is significantly elevated, the results are considered conclusive for gestational diabetes and a GTT may not be recommended.

Diet control and/or insulin injections throughout the rest of the pregnancy may be required to bring glucose levels down to normal levels. In most cases, gestational diabetes will go away after delivery, but women who have gestational diabetes will be at an increased risk of having it again with subsequent children and of developing type 2 diabetes in the future.

Limitations of glucose testing:

In some cases, gestational diabetes may not be detected during the 24 to 28 week gestational period.

Related Test

Glucose

Triple Marker or Quad Marker Screen

Between 15 and 20 weeks gestation, the mother may be given the option to have a screening test for Down syndrome and open neural tube defects, such as spina bifida. Included in the screening panel are tests for alpha-fetoprotein (AFP), human chorionic gonadotropin (hCG), unconjugated estriol, and sometimes inhibin A Â? a relatively new marker that turns the triple test into a quad test. This blood screening panel provides an opportunity to assess the risk of these conditions occurring without performing the more invasive amniocentesis procedure. In most cases, only those patients whose blood screening results indicate a potential problem need to be referred for the amniocentesis.

During the second trimester, it is expected that the levels of AFP and unconjugated estriol will increase, the amount of hCG will decrease, and the amount of inhibin A will stay relatively constant. AFP is produced by the baby and then crosses into the mother’s blood. A baby with a neural tube defect has an opening in its spine or head that allows an increased amount of AFP to pass into the mother’s blood stream. An elevated AFP could also result from multiple fetuses, miscalculation of gestational age, an abdominal wall defect, or for an unknown reason. An ultrasound may be requested to determine the baby’s age and confirm the number of babies. In pregnancies where the fetus is carrying the chromosomal defect that causes Down syndrome, the results of the Triple or Quad Marker Screen tend to show decreased levels of AFP and unconjugated estriol and increased levels of hCG and inhibin A.

The AFP and other test results are interpreted based on the mother’s age, weight, and ethnic background to assess the risk of the child having neural tube defects or chromosomal problems. Of all reported cases of elevated AFP, only a very small percentage of babies truly have a defect. But if the test result is abnormal, a genetic counselor should be consulted to discuss an amniocentesis to further assess the likelihood of a birth defect in the baby.

Limitations of the triple or quad marker screen:

This screening test is not conclusive for the presence of a birth defect but rather predicts the likelihood of a problem. More conclusive tests must be performed to confirm the baby’s condition. Since only a small percentage of pregnancies that have an elevated AFP produce a baby with a problem, parents may undergo undue anxiety.

Related Pages

Triple Screen, hCG

Amniocentesis

Many women have amniocentesis performed, but it is not a routine procedure. It is offered between 15 and 20 weeks gestation to a pregnant woman when:

• she is 35 years of age or older;

• there is a strong family history of a genetic disorder;

• both parents possess a gene for an inherited disorder; or

• the level of maternal alpha-fetoprotein (AFP) is either lower or higher than expected.

Amniocentesis may also be performed after 32 weeks of gestation to help assess the degree of lung development for babies that are at risk of a premature delivery.

Amniocentesis is a procedure used to obtain a small amount of amniotic fluid, which contains AFP produced by the baby and fetal cells. The fetal cells can be tested for chromosomal or genetic abnormalities. A gene analyses may be performed based on family history (i.e., another child born with a defect or with a hemoglobinopathy) or on the results of screening tests performed on the parents (such as for Cystic Fibrosis). Approximately two weeks are needed to complete the testing.

Risks associated with amniocentesis:

There is a slight risk that the needle inserted into the amniotic sac may puncture the baby, cause a small amount of amniotic fluid leakage, cause an infection, and in rare cases may cause a miscarriage.

Limitations of amniocentesis:

An elevated amniotic fluid AFP is not conclusive for neural tube defects.

For certain genetic tests, there is greater reliability of results when testing individuals that are of an ethnic background with a higher prevalence of specific genetic abnormalities.

Not all genetic disorders can be detected.

Third Trimester (28 weeks - delivery)

Testing during this period is primarily directed toward preparation for the birth of a healthy baby and may include:

• Urine screen for sugar and/or protein

• Antibody screen

• Group B streptococcus

• Gonorrhea, chlamydia, and syphilis

• Hemoglobin and platelet count

• Fetal fibronectin (fFN)

Urine Screen for Sugar and/or Protein

At each prenatal visit during this trimester, a urine specimen will be tested for the presence of sugar and/or protein.

Of particular concern during the second and third trimesters is preeclampsia (sometimes called toxemia or pregnancy-induced hypertension), a disorder characterized by high blood pressure and large amounts of protein in the urine that occurs in approximately 8% of all pregnancies. Symptoms include swelling, sudden weight gain, headache, and vision changes. Risk factors include first pregnancy, carrying multiple babies, age (teenagers and women over 40), being African American, and having pre-existing diabetes, hypertension, or kidney disease. It can result in a decrease of air and food getting to the baby through the placenta, causing low birth weight or other complications. If caught early enough, however, through routine checking of blood pressure and urine protein levels, health problems for the mother and baby due to preeclampsia can be prevented.

Antibody Screen (Indirect Antiglobulin Test)

This test is routinely performed on pregnant women who are Rh-negative. It is not unusual for a small number of fetal cells to pass into the mother’s blood stream, which can then cause her to produce an antibody. Although this can occur in all mothers, it is more likely to occur in an Rh-negative mother who has an Rh-positive baby.

At this point in the pregnancy (approximately 28 weeks gestation), a second antibody screen may be requested to see if the mother has developed an antibody that was not detected during the first prenatal visit. If the first antibody screen was negative and the Rh-negative mother has not received a blood transfusion during the pregnancy, then it is most likely that an antibody detected in the second antibody screen is due to exposure to an Rh-positive baby’s red blood cells. This cannot be taken for granted though. If the screen is positive, it must be followed by an antibody identification test to determine which antibody(s) is present.

If the antibody screen is negative for Rh antibodies, then an Rh immune globulin injection (also referred to as RhoGAM), may be given to the Rh-negative mother to prevent her from reacting to the baby’s cells. Additional injections may be administered following invasive procedures, such as amniocentesis or CVS, and following any event where there is the possibility of the baby’s blood transferring to the mother (for example, trauma to the mother’s abdomen). If the mother has already developed the antibody to the Rh factor/antigen, then another injection will not be useful.

Limitations of antibody screen:

An antibody screen will be positive if an Rh immune globulin injection was given within the prior six months. An accurate history of prior Rh immune globulin injections is important in deciding if the positive test is due to the injection or the mother having produced the antibody to the Rh factor.

Related Test

Indirect Antiglobulin Test

Group B Streptococcus

Frequently confused with Group A streptococcus, which causes strep throat, Group B strep is a bacterium that is present in the vagina and gastrointestinal areas of 10% to 30% of pregnant women, though it rarely causes an infection. It is usually not a problem, except when it is present in the vagina during delivery. In this case, it can spread to infect the uterus, amniotic fluid, urinary tract, and any incision made during a cesarean section. At delivery, when the baby passes through the birth canal, the bacteria can be inhaled or ingested.

Infected infants may display symptoms within six hours of birth or as late as two months of age. If untreated, the baby may become septic (infection in blood), develop pneumonia, suffer hearing or vision loss, or develop varying degrees of physical and learning disabilities.

To best assess the risk of infecting the baby at delivery, the mother is screened for Group B strep between 35 and 37 weeks gestation. Specimens from the mother’s vaginal and rectal areas are collected and within 24 to 48 hours the laboratory can determine if Group B strep bacteria are present. If the bacteria are present, or if the woman goes into labor before testing can be completed, it is recommended that the woman receive antibiotics intravenously during labor. Treatment with oral antibiotics taken prior to labor has not proven to be effective in preventing Group B strep infections in the newborn.

Limitations of Group B strep screening:

The screen may not detect a small percentage of women with Group B strep.

Labor may begin before the test results are available.

Gonorrhea, Chlamydia, and Syphilis

It is recommended, and in some states required, that testing for sexually transmitted diseases be performed or repeated in the third trimester.

Hemoglobin and Platelet Count

All women lose a small amount of blood during delivery. Although this is usually not a problem, even a small amount of blood loss can be harmful to women with anemia. A health care provider may want to know the level of hemoglobin in a pregnant woman’s blood prior to delivery to assess the possible impact of the expected blood loss.

Platelets are special cell fragments found in the blood that help form clots to stop bleeding. Women with low platelet counts, or who have platelets that don’t function properly to form clots, are at risk of life-threatening bleeding during delivery. Follow-up testing may be needed to help determine treatment options if a platelet problem is detected.

Related Tests

Hemoglobin, Platelet count, Hematocrit, CBC

Fetal Fibronectin

With fetal fibronectin (fFN) testing, a cervical or vaginal fluid sample is collected and analyzed for fFN, a glycoprotein found at the boundary between the amniotic sac and the lining of the uterus. The test is performed if a woman is 26 to 34 weeks pregnant and having symptoms of premature labor. High levels indicate an increased risk of preterm delivery. Measures can then be taken to delay birth and to help better prepare the fetus for birth. This is because pre-term babies can have potentially serious health complications.

Related Test

fFN

Article Sources

NOTE: This article is based on research that utilizes the sources cited here as well as the collective experience of the Lab Tests Online Editorial Review Board. This article is periodically reviewed by the Editorial Board and may be updated as a result of the review. Any new sources cited will be added to the list and distinguished from the original sources used.

We have included the web address to online sources used in developing and reviewing this article for documentation purposes only. Links included on this Sources page were valid, working links at the time this article was originally prepared, and at each update as indicated here. Please be aware that the source owner may, from time to time, reorganize the source web site, which can result in broken links on our pages. If you wish to access a source and come across a broken link, you may still be able to access it by entering just the parent web address in your browser's address bar (e.g., "www.nih.gov") and then by entering the source title in the site's search feature.

S1

HI5: Pregnancy Tests, ©2000 by AACC

S2

Thomas, Clayton L., Editor (1997). Taber’s Cyclopedic Medical Dictionary. F.A. Davis Company, Philadelphia, PA [18th Edition].

S3

Pagana, Kathleen D.&Pagana, Timothy J. (2001). Mosby’s Diagnostic and Laboratory Test Reference 5th Edition: Mosby, Inc., Saint Louis, MO.

S4

(2002 February). Rubella [19 paragraphs]. March of Dimes Quick Reference Fact Sheets [On-line information]. Available FTP: http://www.marchofdimes.com/professionals/14332_1225.asp

S5

Yen, S. (2003 October 31). Bacterial Vaginosis More Prevalent Than Previously Thought [4 paragraphs]. ACOG News Release [On-line press release]. Available FTP: http://www.acog.org/from_home/publications/press_releases/nr10-31-03-4.cfm

S6

(2002 November 29). ACOG Advises Screening All Pregnant Women for Group B Strep [6 paragraphs]. ACOG News Release [On-line press release]. Available FTP: http://www.acog.org/from_home/publications/press_releases/nr11-29-02-1.cfm

S7

Macones, G., Reviewed (2000 August). Prenatal Tests [62 paragraphs]. KidsHealth for Parents, Nemour Foundation [On-line information]. Available FTP: http://kidshealth.org/parent/system/medical/prenatal_tests.xml

S8

(2005). Your First Tests [19 paragraphs]. March of Dimes [On-line information]. Available FTP: http://www.marchofdimes.com/pnhec/159_519.asp

S9

(2000). Routine Tests During Pregnancy [33 paragraphs]. Medem Medical Library, American College of Obstetricians and Gynecologists [On-line information].

S10

(2000 November). Pre-pregnancy Planning [37 paragraphs]. March of Dimes [On-line information]. Available FTP: http://www.marchofdimes.com/professionals/14332_1156.asp

S11

(2003). Toxoplasmosis, an Important Message for Women [18 paragraphs]. CDC [On-line brochure]. Available FTP: http://www.cdc.gov/ncidod/dpd/parasites/toxoplasmosis/ToxoWomen.pdf

S12

(2002 November). Pregnancy After 35 [28 paragraphs]. March of Dimes Quick Reference and Fact Sheets [On-line information]. Available FTP: http://www.marchofdimes.com/professionals/14332_1155.asp

S13

Ghidini, A. and McLaren, R. (2002 April 18). Patient information: Chorionic villus sampling [27 paragraphs]. UpToDate Patient Information [On-line information]. Available FTP: http://patients.uptodate.com/topic.asp?file=pregnan/7849

S14

Ghidini, A. (2004 November 1). Patient information: Amniocentesis [31 paragraphs]. [On-line information]. Available FTP: http://patients.uptodate.com/topic.asp?file=pregnan/6937

S15

Stewart, D. (2003 July 25, Updated). Genetics [45 paragraphs]. MedlinePlus Medical Encyclopedia [On-line information]. Available FTP: http://www.nlm.nih.gov/medlineplus/ency/article/002048.htm

S16

Norek, S. (1999 June). Common Genetic Diseases in the Ashkenazi Jewish Population [7 paragraphs]. The Jewish Magazine [On-line Magazine Article]. Available FTP: http://www.jewishmag.com/22MAG/disease/disease.htm

S17

(2005). Maternal Serum Screening [22 paragraphs]. ARUP's Guide to Clinical Laboratory Testing [On-line information]. Available FTP: http://www.aruplab.com/guides/clt/tests/clt_a69b.jsp#1208428

S18

Preeclampsia Foundation: About Preeclampsia. Available FTP: http://www.preeclampsia.org/about.asp

S19

Familydoctor.org: Preeclampsia. Available FTP: http://familydoctor.org/064.xml

S20

Medline Plus Medical Encyclopedia: Preeclampsia. Available FTP: http://www.nlm.nih.gov/medlineplus/ency/article/000898.htm

S21

Pagana, Kathleen D.&Pagana, Timothy J. (© 2007). Mosby’s Diagnostic and Laboratory Test Reference 8th Edition: Mosby, Inc., Saint Louis, MO. Pp 651-652.

S22

(2004 June). Maternal Blood Screening for Down Syndrome and Neural Tube Defects [30 paragraphs]. March of Dimes [On-line information]. Accessed on 2/25/07. Available FTP: http://www.marchofdimes.com/professionals/681_1166.asp