Prenatal Tests

You may be offered several prenatal tests throughout your pregnancy. Some tests are performed routinely on all pregnant women, such as blood tests to determine blood type and iron levels. Some tests are done to screen women for a condition they or their baby are at risk for developing. Other tests, such as Chorionic Villus Sampling (CVS) and amniocentesis, are considerations for women 35 years of age and older or those who may be at risk of delivering a baby with certain birth defects. Some tests are done later in pregnancy to measure the baby’s well-being and to make sure that the baby is growing and developing at the expected rate.

The following is a brief description of some of the more common prenatal tests. Your health care provider, and sometimes a genetic counselor, can help you determine which tests might be recommended for your pregnancy and help you when making decisions.

• Routine blood tests
• Quadruple marker
• Expanded Alpha-Fetoprotein (AFP)
• Ultrasound (sonogram)
• Nuchal Translucency (NT) screening
• Chorionic Villus Sampling (CVS)
• Amniocentesis
• Genetic screening
• Third trimester tests for your baby
• Group B Streptococcal Disease (GBS)
• Fetal movement counting

First trimester

Routine blood tests

During your pregnancy, your health care provider will order routine laboratory tests that require small samples of blood be drawn.

Blood tests are performed to determine/screen for:

• Blood type (A, B, AB or O)
• Rh factor (Rh positive or Rh negative)
• Anemia
• Rubella immunity status
• Diabetes
• Hepatitis
• Human Immunodeficiency Virus (HIV, the virus that cause Aquired Immunodeficiency Syndrome, or AIDS)
• Sexually transmitted diseases as recommended by your health care provider

Sexually Transmitted Diseases (STDs)/Drug Testing
Your health care provider may recommend other studies be done during your pregnancy to screen for sexually transmitted diseases (STDs) and/or drugs. Some of the most common STDs include:

• Gonorrhea
• Chlamydia
• Genital herpes
• Trichomoniasis

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Second trimester

Quadruple marker

The quadruple marker is a screening procedure that measures the amount of four substances in your blood:

• Alph-fetoprotein (AFP)
• Unconjugated estriol(uEST)
• Human chorionic gonadotropin (hCG)
• Analyte inhibin (Inh)

Studies show that women with pregnancies affected with Down syndrome have lower serum of AFP and uEST and higher levels of hCG than women with unaffected pregnancies.

The tests can be done using a small sample of your blood sometime between 15 and 20 weeks of pregnancy, counting from your last menstrual period. Results are usually available in 1 to 2 weeks. If the results are abnormal, further testing (such as ultrasound and amniocentesis) may be suggested.

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Expanded Alpha-Fetoprotein (AFP)

Expanded AFP is a simple blood test performed between 15 and 20 weeks of pregnancy. The test provides information about the risk of neural tube defects, such as spina bifida, Down syndrome and other genetic problems.

Frequently asked questions about Expanded AFP

• Who should consider Expanded AFP?
  The state of California recommends that this test be offered to all pregnant women.



• How is the screening performed?
  The test is performed through a simple blood test ordered by your health care provider.



• What type of problems can be detected?
  The test provides information about the risk of neural tube defects, such as spina bifida, and chromosome disorders in the developing baby.



• Is the blood test ever wrong?
  It is important to note that the Expanded AFP test is only a screening test, not a diagnostic test. There will be a group of women who receive a false positive or “false alarm.” Most women who test positive are carrying a healthy baby. The only way to tell a false positive result from a true birth defect is through diagnostic testing. Women with a positive test result are offered amniocentesis as a diagnostic test. A genetic counselor can help explain the benefits and limitations of the Expanded AFP blood test compared to diagnostic tests.

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Ultrasound (sonogram)

In an ultrasound procedure, a device known as a transducer is placed on your abdomen. The device directs high frequency sound waves at your developing baby. The echoes created by the sound waves are turned into visual images of the baby’s limbs, organs and other internal structures that can be seen on a monitor.

Frequently asked questions about ultrasound:

• Will an ultrasound hurt the baby?
  Extensive studies to date show no evidence of ill effects or harm to the baby by these sound waves.



• What can ultrasound detect?
  An ultrasound test can detect:
  • Many birth defects early in pregnancy that otherwise would go undetected until birth
  • Number of babies present
  • Baby’s growth
  • Confirmation of due date
  • Placental position
  • Other information about your pregnancy that can be useful to you and your health care provider


• What is a fetal echocardiogram?
  A fetal echocardiogram is a detailed ultrasound evaluation of the baby’s heart structure. It is performed in pregnancies at increased risk for congenital heart disease. Fetal echocardiograms can detect most cases of serious, life threatening congenital heart problems.



• What is a targeted ultrasound examination?
  A targeted ultrasound examination looks at a specific organ system or part of the body. It is used to try to detect any trouble before birth in pregnancies at increased risk for specific genetic or physical problems. As with many medical tests, ultrasound is not perfect. Because of factors that can develop later in pregnancy or interfere with the ability to clearly see all of the baby’s internal structures, an ultrasound will not detect all birth defects.



• Does an ultrasound hurt?
  You should not feel pain of any kind as this is a non-invasive test.

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Additional testing
You may be advised by your health care provider that you need additional tests such as:

Nuchal Translucency (NT) screening

Nuchal translucency (NT) screening is a non-invasive screening test used to determine the risk of Down syndrome. It can be performed early in pregnancy, between 11-1/2 and 13 weeks, and is available to women of all ages.

Frequently asked questions about NT screening:

• How is NT screening performed?
  NT screening is a high-resolution ultrasound examination of the baby’s nuchal area (a fold of skin at the back of the neck). The results are combined with the mother’s age to determine the risk for Down syndrome.



• Will the test detect all cases of Down syndrome?
  The detection rate for Down syndrome is about 80 percent for NT screening. A woman then has the option of undergoing CVS or amniocentesis for a more definitive diagnosis.



• Will this test identify Spina Bifida?
  No. The ultrasound is performed too early to reliably detect this disorder.



• Can you get NT screening anywhere?
  No. The screening is only available at centers that have been trained by and participate in ongoing quality assurance programs sponsored by the Fetal Medicine Foundation in London.

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Chorionic Villus Sampling (CVS)

CVS is a procedure in which a small amount of tissue (chorionic villi) is obtained from the developing placenta between 10 and 12 weeks of pregnancy. The tissue is analyzed for chromosome disorders and, if indicated, specific genetic diseases.

On the positive side, CVS is performed much earlier in pregnancy than amniocentesis. On the negative side, CVS does not detect neural tube defects. However, an AFP test and a high resolution ultrasound examination can be performed later in pregnancy to screen for these defects.

Frequently asked questions about CVS:

• How is CVS done?
  An ultrasound examination is performed first to date the pregnancy and locate the developing placenta. The CVS sample can be obtained in two ways depending on the structure of the uterus and the position of the placenta. During transcervical CVS, a thin hollow tube is inserted through the vagina and cervix to reach the chorionic villi. Ultrasound is used to guide the tube to the edge of the developing placenta. A small amount of tissue is removed through the tube. Transabdominal CVS is similar to amniocentesis. Guided by ultrasound, a thin needle is inserted through the mother’s abdominal wall to obtain a small amount of chorionic villi. Both procedures usually take just a few minutes.



• Does CVS hurt??
  Some women say the procedure is uncomfortable. Most women are able to return to their regular activities the day after CVS.



• Does CVS have any side effects?
  Some women experience spotting, bleeding or cramping following CVS. These usually go away without difficulty. The following is recommended after undergoing CVS:
  • No lifting over 15 pounds for 24 hours
  • No strenuous exercise for 72 hours
  • No air travel for 72 hours
  • No sexual intercourse for 72 hours
  
  There is a natural miscarriage rate throughout any pregnancy.

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Amniocentesis

Amniocentesis is a procedure in which a small amount of amniotic fluid is obtained between 15 and 17 weeks of pregnancy and then analyzed. Chromosome studies are done on cells contained in the fluid for conditions such as Down syndrome. Amniotic fluid also assists in screening for neural tube defects, such as spina bifida and genetic disorders such as sickle cell anemia.

Frequently asked questions about amniocentesis:

• How is amniocentesis done?
  An ultrasound examination is done first to date the pregnancy and locate the placenta and the amniotic fluid surrounding the baby. With ultrasound guidance, a needle is inserted through the mother’s abdominal wall into the amniotic fluid. A small amount of fluid is removed and sent for analysis. The entire procedure usually takes just a few minutes.



• Does the procedure hurt?
  Some women say the procedure is uncomfortable, although many women say the sensation is like a routine blood draw. If desired, a local anesthetic can be used to numb the skin before the needle is inserted. Some women do experience cramping after the test. Most women are able to return to their regular activities the day after amniocentesis.



• Does amniocentesis have any side effects
  Some women experience vaginal fluid loss, cramping, and a small amount of vaginal bleeding. This should resolve quickly and go away without further complications. The following is recommended after undergoing amniocentesis:
  • No lifting over 15 pounds for 24 hours
  • No strenuous exercise for 72 hours
  • No air travel for 72 hours
  • No sexual intercourse for 72 hours
  
  There is a natural miscarriage rate throughout any pregnancy. Amniocentesis increases this natural complication rate for this period of pregnancy by less than .02 to .03 percent. That is, less than 1 in 300 to 500 women would have a miscarriage as a result of amniocentesis.



• When should I be worried about symptoms after the procedure?
  Call your doctor if:
  • You have cramps, leaking of fluid, or vaginal bleeding that does not go away or is getting worse
  • You have a fever higher than 100.4 F (58 C)
  
  
• What types of problems can be detected by amniocentesis?
  Careful study of the cells contained in the amniotic fluid will identify chromosome problems, such as Down syndrome. Measurement of the protein in the amniotic fluid, called Alpha Fetoprotein (AFP), will detect the majority of neural tube defects, such as spina bifida. When a history of genetic disease is known in a family, specific testing may be available through DNA or enzyme testing.
  
  No method of prenatal testing can guarantee that a baby will be born without birth defects, genetic disease or mental retardation.



• How long will it take for test results?
  Results of the chromosome study and AFP measurement are usually available in less than two weeks. Special studies may take longer.



• Are the amniocentesis results accurate?
  Chromosome results are greater than 99 percent accurate and measurement of the AFP detects approximately 95 percent of neural tube defects. DNA and enzyme studies also have high accuracy.
  
  Occasionally, test results need to be clarified through further ultrasound evaluations or blood tests on both parents. A repeat amniocentesis or fetal blood sampling is rarely needed.

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Genetic screening

Some people may have an increased chance of being a carrier of certain genetic diseases based on their ethnic backgrounds. Examples include:

• Cystic Fibrosis in Caucasians (whites)
• Sickle cell disease in African Americans
• Thalassemia in Asians and individuals of Mediterranean descent
• Tay-Sachs in Canavan disease in Ashkenazi Jews.

Other people may be at risk for an inherited disorder present in their family. If you are concerned that your baby may be at risk for inheriting a disorder, talk with your health care provider. Your health care provider or a genetic counselor can discuss what screening options may be appropriate for you.

If you are at risk, a simple blood test may determine if you or your partner are carriers. If either of you are carriers, your health care provider or genetic counselor can discuss the risk to your baby of inheriting a disorder.

Cystic Fibrosis (CF)
Cystic Fibrosis is one of the most common inherited diseases. About 1 in 2,500 Caucasians in the United States has CF. Although it can occur in other ethnic groups, it is less common. CF causes the body to produce large amounts of abnormally thick mucus, which collects in the lungs and leads to congestion, pneumonia and lengthy hospitalizations. Mucus may also collect in the intestines, resulting in diarrhea and poor growth. Although present from birth, CF symptoms may not appear until a later time. CF does not affect intelligence, but it does greatly shorten life span. Presently, there is no cure for CF.

Sickle cell disease
Most sickle cell disease occurs among African Americans and Hispanics of Caribbean descent. About one in every 400 African Americans has sickle cell disease. Sickle cell is curable only in rare cases.

Sickle cell disease is an inherited disease of the red blood cells that can cause severe pain and damage to vital organs. Infants and young children with the disease are especially vulnerable to severe bacterial infections, the leading cause of death in sickle cell cases.

There are several forms of sickle cell disease. The most common forms are referred to as:

• SS: the child inherits two sickle cell genes
• SC: the child inherits one sickle cell gene and one gene for another abnormal type of hemoglobin (the oxygen-carrying part of the red blood cell)
• S beta-zero: the child inherits one sickle cell gene and one gene for a type of thalassemia, another inherited anemia

Thalassemia
Thalassemia occurs most frequently in people of Italian, Greek, Middle Eastern, Asian and African descent. Thalassemia includes a number of different forms of anemia (red blood cell deficiency). The two main types are called alpha and beta thalassemias, depending on which part of an oxygen carrying protein is lacking in the red blood cells.

Thalassemia major is the most harmful form. Most children born with this kind of thalassemia appear healthy at birth, but during the first year or two of life they become pale, listless, fussy, have a poor appetite and get many infections. Without treatment, the spleen, liver and heart soon become enlarged, bones become brittle, and the facial bones become distorted. Treatment consists of frequent blood transfusions to lessen the effects of the disease. Children born with thalassemia minor have very mild symptoms or none at all and require little to no treatment.

Tay-Sachs
Tay-Sachs occurs most often in descendants of Central and Eastern European (Ashkenazi) Jews and French Canadians. Tay-Sachs is a neurological disease that begins during infancy and gets worse over time. It is caused by a deficiency of the enzyme Hexosaminidase A (Hex A) necessary for breaking down certain fatty substances in brain and nerve cells. Without this enzyme, the entire central nervous system eventually stops working. Typically, a baby with Tay-Sachs develops normally for several months. Progressive deterioration then causes blindness, deafness, seizures and paralysis. Children do not usually live beyond the age of five. There is currently no treatment or cure for this disease.

Canavan
Canavan disease occurs most frequently in descendants of Central and Eastern European (Ashkenazi) Jews. Canavan is a progressive neurological disease caused by a deficiency of the enzyme Asparto-acyclase. This enzyme is crucial to the brain’s normal functioning. Typically, a baby with Canavan disease appears normal at birth. After several months of life, a progressive deterioration begins causing mental retardation, muscle weakness that develops into muscle stiffness, blindness, seizures and feeding problems. Children usually do not live beyond the age of 10. There is no cure or treatment for this disease.

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Third trimester tests for your baby

Nonstress Test (NST)
A NST helps determine your baby’s well-being. An electronic fetal monitor is used to trace your baby’s heart rate to see if it speeds up or slows down as the baby moves.

Contraction Stress Test (CST)
A CST helps determine how well your baby will handle the stress of labor. During a CST, your nipples are stimulated to release oxytocin which causes your uterus to contract. An electronic fetal monitor is used to trace your baby’s heart rate and look for changes in relation to your uterine contractions.

Oxytocin Challenge Test (OCT)
An OCT is the same as a CST except contractions are brought on by a small dose of pitocin, a synthetic form of the hormone oxytocin, administered through a vein in your arm. An OCT is usually done if the contractions from nipple stimulation are not strong enough to assess how your baby will handle the stress of labor.

Biophysical Profile (BPP)
A BPP is a test of your baby’s well-being and may be done later in your pregnancy. Abdominal ultrasound is used to assess your baby’s heartbeat, movement and breathing pattern, along with the placenta and amount of amniotic fluid. BPP is considered an “in utero” check-up of your baby.

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Group B Streptococcal Disease (GBS)

GBS is a bacteria that is naturally present in the gastrointestinal (GI) tract. Sometimes in pregnancy, GBS may get into and grow in the rectal area or vagina (1 in 7 women). If GBS is not detected and treated with antibiotics, it may transfer to the baby and place the baby at risk for serious infection (1 per 150 births) or even death (1 per 1,000 births).

To test if GBS is growing in your vagina or rectum, your health care provider should culture these areas between 35 and 37 weeks of pregnancy according to the most recent recommendations. If GBS is present, antibiotics can be given during labor, which greatly reduces the above mentioned complications.

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Fetal movement counting

From 28 weeks of pregnancy until delivery, one of the best ways to keep track of a healthy baby is by counting the baby’s movements. Healthy babies are very active, especially in the evening after dinner. However, some perfectly normal babies may sleep quietly for as long as 60 minutes without moving. Babies are usually sluggish and move less when they are having problems. Counting your baby’s movements can warn you and your health care provider of any developing problems.

The following instructions can help you and your health care provider be sure that your baby is feeling well.

• You may count at any time of the day, when you feel your baby is more active. For most women, this is in the evening after dinner when you are lying down and quiet. Get into a position that you normally feel your baby move. Lying on your side is best. Record the time that you start counting.
• Count ten separate times that the baby moves. A movement may be a kick, turn or flip of the baby.
• Record the time you feel the 10th movement. If you count 10 movements in less than two hours, stop counting until tomorrow.

If you do not feel 10 movements in two hours, call your health care provider.

Remember:

• Your baby may move all 10 time in 1/2 hour or less.
• Your baby may take up to two hours to move 10 times.
• The important thing is to know what is normal for your baby so you can tell your health care provider if something different happens.

Call your health care provider if:

• You do not feel 10 movements in two hours.
• You have not felt the baby move all day.
• It takes longer and longer each evening to get to the 10th movement.

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