Mayo Clinic Guide to a Healthy Pregnancy: From Doctors Who Are Parents, Too!

CHAPTER 21. Prenatal testing

As you look forward to your baby’s arrival, you may be wondering about a number of things. Will you have a girl or a boy? Will he have blue eyes or brown eyes? Will she be funny like her dad, smart like her mom? How will it feel to finally hold your baby in your arms?

Along with feelings of excitement and joy, you may have moments of doubt and anxiety. What if something goes wrong with the pregnancy? Will your baby be healthy? These are completely normal feelings experienced by most pregnant women. It may reassure you to know that most pregnancies — more than 95 percent — are healthy and result in the safe delivery of a healthy baby.

Still, in some instances you may wish to know specific information about your baby’s health before his or her birth. Perhaps because of your age or family history you may be at increased risk of carrying a baby with a chromosomal problem or some other genetic disorder. Whatever the reason, certain tests can help determine the health of your baby while he or she is still in your womb. These are called prenatal tests.

Basically, two types of prenatal tests are used during pregnancy:

 Screening tests. These are safe, relatively inexpensive tests that are offered to all pregnant women, regardless of age or other risk factors. Screening tests are meant to identify women who are more likely to be at risk of certain conditions and who might benefit from more narrowly focused diagnostic tests. Screening tests aren’t required, but your care provider will probably ask whether you want to be tested.

 Diagnostic tests. Diagnostic tests are usually done when a screening test has indicated a possible problem or when you or your baby is at increased risk of a certain condition. They can provide enough information to diagnose a medical condition while the baby is still in the uterus. These tests are generally more invasive, more expensive and slightly riskier than are screening tests. It’s your decision if you want this type of testing.

ISSUES TO CONSIDER

Prenatal tests are voluntary. Each test has its own risks and benefits, so it’s worthwhile to know about these tests so that you can make an informed decision. Before you undergo a prenatal test, think about what information the test will provide and how you will use the information. Many, but not all, women choose to undergo basic ultrasounds and blood tests. Most women don’t undergo the more detailed diagnostic tests because most pregnancies don’t carry a high risk of complications.

6 key questions Before scheduling a prenatal test, you and your partner might want to consider these questions:

1. What will you do with the information once you have it? How will it affect decisions regarding your pregnancy? Most results from prenatal testing come back normal, which can help ease any anxiety you may be feeling. If a test indicates that your baby may have a birth defect or another health condition, how will you handle it? You may be faced with decisions you never expected to have to make, such as whether to continue the pregnancy. On the other hand, knowing about a problem ahead of time may give you the option of planning for your baby’s care in advance. In any case, it’s OK to say no to a test if you feel it won’t provide you with useful information or it won’t affect the way you handle your pregnancy.

2. Will the information provide better care or treatment during pregnancy or delivery? At times, prenatal testing can provide information that affects your care. Testing may uncover a problem with your baby that doctors can treat while you’re pregnant. It may alert your care provider to a problem that requires a specialist to treat your baby right after he or she is born.

3. How accurate are the results of the test? Prenatal tests aren’t perfect. Even if the result of a screening test is negative — meaning that your baby is at low risk of having a certain condition — there’s still a small chance that the condition is present. This is known as a false-negative test result. Just the opposite, a screening test may produce a positive result, placing you in a higher risk group. But it’s possible, or even likely, that no disease exists. This is called a false-positive test result. The proportion of false-negative and false-positive results varies from test to test. Be sure to discuss the accuracy of each test with your care provider.

4. Will undergoing a test be worth the anxiety it may cause? Screening tests identify women at risk of certain conditions. Even if a test indicates a risk, the majority of women will have a healthy baby. Thus, a screening test may cause unnecessary anxiety.

5. What are the risks of the procedure? You may want to weigh the risks of the tests, such as pain or possible miscarriage, against the value of learning the information.

6. How much does the test cost? Is it covered by your health insurance? Tests that aren’t medically necessary may not be covered by insurance. In some cases, a social worker or genetic counselor may help you get information about financial assistance, if necessary. If financial help isn’t available, are you willing and able to cover the cost of the test?

THE TESTS

Following is a detailed list of the tests you might encounter during your pregnancy, from the routine to the optional. This information can function as a handy go-to guide for basic information on each test. But be sure to talk with your care provider about the tests you’re considering. He or she can give you the best risk-and-benefit assessment, based on your individual circumstances.

Ultrasound The ultrasound exam is probably the prenatal test you’ve heard the most about. Your care provider uses ultrasound imaging to get a picture of your unborn baby and determine how your pregnancy is progressing. Usually, you’re able to see images of your baby while the test is being done. Ultrasound can also be used to diagnose some types of birth defects, such as a spinal abnormality (neural tube defect), heart defects or other abnormalities.

The ultrasound exam uses sound waves as energy. The transducer, which is placed on your abdomen, produces high-frequency sound waves that humans cannot hear. The sound waves bounce off tissues in your body, including the baby, and back to the transducer. They return to the transducer at different times with different qualities, depending on the density of the tissue and its distance from the transducer. As the signals return, they’re converted into an image, which is viewed on a monitor. Several different types of ultrasound examinations are available:

 Standard ultrasound. This type of ultrasound creates two-dimensional (2-D) images that can give your care provider information about your pregnancy. It can be used to determine the age of your baby, how he or she is developing, the location of the placenta, and the relationship between your body and the baby. It usually lasts about 20 minutes.

An ultrasound image creates a picture of the baby that can provide valuable information about your pregnancy.

 Advanced ultrasound. Also called a targeted ultrasound or a level II ultrasound, this type of testing is often used to explore a suspected abnormality found during a standard ultrasound or a screening test. The exam is more thorough and may use more sophisticated equipment. It’s also longer, taking from 30 minutes to over an hour. Your care provider also may recommend this type of ultrasound if you have a high-risk pregnancy. This ultrasound can be used to view your baby’s head, spine and other organs in detail, and it’s highly effective at diagnosing neural tube defects.

 Transvaginal ultrasound. In early pregnancy, your uterus and fallopian tubes are closer to your vagina than to your abdominal surface. If you have an ultrasound during your first trimester, your care provider may opt for a transvaginal scan. It provides a clearer picture of your baby and the structures around your baby. This type of ultrasound may also be used to detect problems with your cervix during pregnancy. A transvaginal ultrasound uses a slender, wand-like device that’s placed inside your vagina.

 Three-dimensional (3-D) ultrasound. There are two types of 3-D ultrasound. One type, called surface rendering, creates an image of baby similar to a black and white photograph. In the other type, called volume capture, a set of 3-D ultrasound data is analyzed after examination — similar to what is done with CT scans and MRIs — to enhance diagnosis.

 Doppler ultrasound. Doppler imaging measures changes in the frequency of the ultrasound waves as they bounce off moving objects, such as blood cells. It can measure the speed and direction at which blood circulates. With it, care providers can determine how much resistance there is to the flow of blood through various tissues. If you have complications of pregnancy, such as high blood pressure or preeclampsia, a Doppler ultrasound may help determine if there are problems with blood flow to the baby or the placenta.

 Fetal echocardiography. This type of exam uses ultrasound waves to provide a more detailed picture of your baby’s heart. It focuses on the heart’s anatomy and function and may be used to confirm or rule out a congenital heart defect.

When and how it’s done An ultrasound exam can be done at any time during your pregnancy. An ultrasound during the first trimester is generally performed to verify that the baby is alive and well and to determine his or her age. It can also be used as part of a screening test performed in the first trimester (first trimester screening).

Most often an ultrasound is performed between the 18th and 20th weeks of pregnancy. At this stage in pregnancy, an ultrasound exam can detect structural abnormalities, in addition to verifying the baby’s age. Your baby has developed enough at this point so that his or her skeletal structure and organs can be identified, and all four chambers of the heart and the major arteries can be seen.

In some situations, such as a high-risk pregnancy, ultrasounds may be repeated throughout the pregnancy. They can be used to monitor the health of both the mother and the baby and to track the baby’s growth.

Depending on the stage of your pregnancy when the ultrasound is performed and the practice at the institution where you have the exam, you may be asked to arrive for your exam with a full bladder.

Once in the exam room, you will be asked to lie on your back and a gel will be applied to your abdominal area. The gel acts as a conductor for sound waves and helps to eliminate air bubbles between the transducer and your skin. The transducer is a small plastic device that sends out the sound waves and records them as they bounce back.

During the exam, the person administering the test moves the transducer back and forth over your abdomen, directing sound waves into the uterus. Depending on your baby’s age and position, you may be able to make out a face, tiny hands and fingers, or arms and legs. Throughout the exam, your care provider will stop to measure the baby’s head, abdomen, thighbone and other structures. These measurements help your care provider determine your baby’s growth. Pictures may also be taken of important structures such as the heart.

Unlike an X-ray, an ultrasound examination doesn’t involve radiation. Forty years of use has not raised any concerns that ultrasound causes harm to mothers or babies.

What the results may tell you Based on the images produced by the exam, your care provider can determine a number of things about your pregnancy and your baby, including:

 That you are indeed pregnant.

 How many weeks it’s been since conception (baby’s gestational age).

 The number of babies you’re carrying.

 Your baby’s growth and development.

 Your baby’s movement, breathing and heart rate.

 The location of the pregnancy. Sometimes a pregnancy develops outside the uterus (ectopic pregnancy), usually in the fallopian tube. This can be a medical emergency.

 Structural variations or abnormalities in your baby.

 The location and development of the placenta.

 Whether you’ve had a miscarriage.

 Assessment of the cervix and the possible risk of preterm delivery.

 Measures of fetal well-being such as the volume of fluid around the baby, muscle tone and activity.

 The sex of your baby. Being able to determine what sex your baby is depends on the baby’s position in the uterus and the position of the umbilical cord. Decide in advance if you want to know this information. You can ask in advance that the sex of the baby not be revealed to you.

Reasons to have it done For most pregnant women, an ultrasound exam basically confirms assumptions regarding baby’s due date and health. But because it’s an important screening test for identifying inaccurate dating, multiple pregnancies and placental disease, most care providers wouldn’t due without it.

If concerns do develop, however, ultrasound is often the best tool to address those concerns. If you’re not sure when you became pregnant, an ultrasound can determine the baby’s gestational age. If screening tests indicate an abnormality, an ultrasound may be able to identify it. If there’s any bleeding or a concern about the baby’s growth rate, an ultrasound is the best initial test. In addition, ultrasound imaging can be used to guide your care provider while performing other prenatal tests, such as amniocentesis or chorionic villus sampling.

Many women and their partners look forward to an ultrasound because it gives them a first glimpse of their baby or a chance to find out the sex of their baby. However, having an ultrasound solely to determine the sex of your baby generally isn’t recommended.

Accuracy and limitations of the test Although ultrasound is a useful imaging tool, it can’t detect all fetal abnormalities. If an ultrasound can’t offer an explanation for a perceived problem, your care provider may recommend other diagnostic imaging or testing, including magnetic resonance imaging (MRI), amniocentesis or chorionic villus sampling (CVS).

First trimester screening First trimester screening involves a two-step process that offers early information on your baby’s health:

 Blood test. It measures levels of two pregnancy-specific substances, pregnancy-associated plasma protein A (PAPP-A) and beta human chorionic gonadotropin (beta-HCG).

 Ultrasound exam. This test is done to measure the size of the clear space in the tissue at the back of a baby’s neck (nuchal translucency). A vaginal ultrasound is often used for this assessment.

Your care provider uses the results of these tests to screen for:

 Down syndrome (trisomy 21). This is a genetic condition that causes mental retardation and other medical problems. In the vast majority of cases, the fetus has three copies of chromosome 21, instead of two copies.

 Trisomy 18. This is a chromosomal abnormality characterized by three number 18 chromosomes. Trisomy 18 typically causes severe deformity and mental retardation. Most babies with trisomy 18 die before birth or within their first year. The risk of having a baby with trisomy 18 is very low.

A first trimester screen may heighten suspicion regarding a potential heart defect or skeletal problem, but the test isn’t done for this purpose.

When and how it’s done Typically, first trimester screening is done between weeks 11 and 14 of pregnancy, earlier than many other prenatal tests. For the blood test, a sample of blood is taken from a vein in your arm and sent to a lab for analysis.

During the ultrasound exam, your care provider or a technician uses the images acquired to measure the size of the clear space in the tissue at the back of your baby’s neck. This test may take up to an hour.

First trimester screening poses no risk of miscarriage and isn’t known to cause other pregnancy complications.

What the results may tell you Your care provider will use the test results to help gauge your risk of carrying a baby with Down syndrome or trisomy 18. Other factors, such as your age and personal or family health history, also may affect your risk.

First trimester screening results are given as positive or negative and also as a probability, such as a 1 in 5,000 risk of carrying a baby who has Down syndrome. Generally, the test is considered positive for Down syndrome if the risk is 1 in 230 or greater (the exact number may vary slightly with different laboratories). For trisomy 18, the test is considered positive if the risk is 1 in 100 or greater.

Reasons to have it done Because first trimester screening can be done earlier than most other prenatal screening tests, you’ll have the results early in your pregnancy. This gives you more time to make decisions about further diagnostic tests, the need for expert counseling, and the course of your pregnancy. If your baby is diagnosed with a genetic condition, you’ll also have more time to prepare for the possibility of caring for a child who has special needs.

If you do undergo first trimester screening, you may be faced with the decision of whether to undergo further testing based on the results. Before the screening, consider what level of risk would be enough for you to choose additional testing. Follow-up diagnostic tests provide more information, but they’re more invasive.

Accuracy and limitations of the test First trimester screening correctly identifies about 85 percent of women who are carrying a baby with Down syndrome. About 5 percent of women have a false-positive result, meaning that the test result is positive, but the baby doesn’t actually have Down syndrome. For trisomy 18, the detection rate is approximately 90 percent with a 2 percent false-positive rate.

Second trimester screening, or quad screening The quadruple screening test, also known as the quad screen, measures levels of four substances in a pregnant woman’s blood:

 Alpha-fetoprotein (AFP), a protein made by the baby’s liver

 Human chorionic gonadotropin (HCG), a hormone made by the placenta

 Estriol, a hormone made by the placenta and the baby’s liver

 Inhibin A, another hormone made by the placenta

The quad screen evaluates your risk of carrying a baby with developmental or chromosomal conditions, such as:

 Spina bifida. This condition occurs when the tissue surrounding a baby’s developing spinal cord doesn’t close properly. It may be associated with mental retardation and paralysis.

 Anencephaly. It results when tissue fails to cover the baby’s brain and head. A baby born with anencephaly may be stillborn or die within a few hours or days after birth.

 Down syndrome (trisomy 21). This abnormality causes mental retardation and other medical problems.

 Trisomy 18. This is a chromosomal disorder caused by an extra copy of chromosome 18. Fetuses with trisomy 18 have multiple abnormalities, and the disorder is almost always fatal.

A similar test known as the triple screen — which only checks AFP, HCG and estriol — is may be offered in place of the quad screen. However, results of the quad screen are slightly more reliable.

When and how it’s done Ideally, the quad screen is performed between weeks 15 and 18 of your pregnancy, but may be done as late as 22 weeks. Levels of the chemicals measured change substantially as your baby continues to develop, so it’s critical that the calculated age of your baby is correct. The AFP test is most accurate when done between the 16th and 18th weeks of gestation. For the screen, a member of your health care team takes a sample of blood from a vein in your arm, which is sent to a lab for analysis.

The quad screen doesn’t pose any risk of miscarriage or other pregnancy complications. The biggest issue for most mothers is the anxiety caused by waiting for the test results. About 5 percent of the time, results will be positive, and additional, more invasive and riskier tests will be offered. Still, most women within this positive group have unaffected babies.

What the results may tell you A positive quad screen simply means that levels of some or all of the substances measured in your blood were outside the normal range. This can indicate a potential problem that may need follow-up testing. However, positive results can occur for various reasons, including:

 Inaccurate dating (miscalculation of how long you’ve been pregnant)

 A multiple pregnancy

 In vitro fertilization

 The presence of other medical conditions, such as diabetes

 Maternal smoking

Reasons to have it done Some care providers use the quad screen to follow up on the results of first trimester screening. Analyzing the results of these two tests together can provide greater accuracy. The downside is that you may have to wait until both tests are completed and analyzed before learning the final results.

If you didn’t have the first trimester screening, the quad screen offers another chance to obtain an assessment of your risk of carrying a baby with chromosomal or anatomical abnormalities. Negative results may give you peace of mind. If you receive positive results, you can talk to your care provider or a genetic counselor about your options.

Accuracy and limitations of the test The quad screen correctly identifies about 80 percent of women who are carrying a baby who has Down syndrome. Approximately 6 to 7 percent of women have a false-positive result, meaning that the test result is positive but the baby doesn’t actually have Down syndrome.

Amniocentesis Amniocentesis is a diagnostic test often used to follow up on abnormal results obtained from a screening test. With amniocentesis, a small sample of amniotic fluid is withdrawn from the sac surrounding your baby. The amniotic fluid is a clear liquid that envelops your baby in the uterus and provides a cushion. Amniotic fluid consists mostly of urine from your baby but also contains cells that your baby has shed and proteins made by the baby. These cells can provide genetic and other information about your baby.

The two common types of amniocentesis are:

 Genetic amniocentesis. The cells taken from the amniotic fluid sample can be collected and grown in a laboratory (cell culture). From that culture, the chromosomes and genes can be checked for abnormalities, such as Down syndrome. The alpha-fetoprotein (AFP) level in the amniotic fluid sample can also be tested for signs of neural tube defects, such as spina bifida. In families with certain known genetic disorders, amniotic fluid may also be collected for other highly specialized tests.

During genetic amniocentesis, an ultrasound transducer shows on a screen the positions of your fetus and the needle, enabling your doctor to safely withdraw a sample of amniotic fluid for testing.

 Maturity amniocentesis. With this test, the fluid is analyzed to find out if the baby’s lungs are mature enough to function normally at birth.

When and how it’s done Genetic amniocentesis can be done at any time during pregnancy, but is usually performed between the 15th and 20th weeks of gestation. At this point, your uterus generally contains enough amniotic fluid, and there’s decreased likelihood of fluid leakage. Doing the test earlier may increase the risk of a pregnancy loss.

Maturity amniocentesis is done when there may be a reason to deliver the baby before the due date. It’s usually done between 34 to 39 weeks of gestation.

The test can be performed in your doctor’s office. Ultrasound is used to determine the position of the fetus. Guided by the ultrasound images, your doctor inserts a thin, hollow needle through your abdomen and into your uterus. About 2 to 4 teaspoons of amniotic fluid are withdrawn into a syringe and sent to a laboratory for analysis. The procedure is over when the needle is removed.

Many women find that the procedure isn’t as painful as they had anticipated. You’ll notice a stinging sensation or a prick when the needle enters your skin and some menstrual-like cramping during the procedure.

Although amniocentesis is a relatively safe test, it carries a few risks:

 Miscarriage. Amniocentesis done before 24 weeks of gestation carries a risk of miscarriage of about 1 in 300 to 1 in 500. The risk of all complications, including minor complications, is approximately 1 to 2 percent. Amniocentesis performed early in the pregnancy — prior to 14 weeks — carries a higher risk of miscarriage. Amniocentesis performed to check maturity has almost no risk of pregnancy loss.

 Post-procedural complications. You may have cramping, bleeding or leaking of amniotic fluid after the procedure. Bleeding occurs in 2 to 3 percent of cases and generally goes away without treatment. In as many as 1 percent of cases of early genetic amniocentesis, amniotic fluid leakage occurs, which can cause miscarriage.

 Rh sensitization. In a few cases, amniocentesis may cause fetal blood cells to cross the placenta into the maternal blood stream. If this happens and your blood type is rhesus (Rh) negative and your baby’s is Rh positive, it may lead to Rh disease, which can be fatal to subsequent babies. If you’re Rh negative, your doctor will treat you with medication to prevent this.

 Needle injury. There’s a slight chance the baby may be punctured by the needle, though use of the ultrasound for guidance makes this rare. If it happens, the outcome is usually no more serious than a diaper pin prick.

What the results may tell you Genetic amniocentesis can tell you if your baby has a chromosomal abnormality, such as Down syndrome; a genetic disorder, such as cystic fibrosis; or a neural tubal defect, such as spina bifida.

In addition to lung maturity, other uses of amniocentesis include checking for anemia in a baby due to rhesus (Rh) incompatibility and intrauterine infection. If you don’t have a type of protein called Rh factor in your blood (are negative), but your baby does (is positive), you have a condition called Rh incompatibility. Amniocentesis can be used to determine whether and how much your baby is affected. In order to determine whether you have an infection caused by a viral agent or parasite, such as toxoplasmosis, your doctor may need a sample of the amniotic fluid for analysis.

Reasons to have it done The decision to have a genetic amniocentesis can be very difficult. Talk to your care provider or a genetic counselor about your options. Reasons to consider the test may include:

 Abnormal results from a screening test, such as the first trimester screen.

 Either parent has a chromosomal abnormality.

 Either parent carries a chromosome rearrangement that doesn’t affect him or her but may affect the child.

 You’ll be 35 or older when you have the baby. The older you are, the higher your baby’s risk of having a chromosomal abnormality.

 Either parent has a central nervous system defect such as spina bifida or a blood relative with such a problem.

 A previous pregnancy complicated by a chromosomal abnormality or neural tube defect.

 Parents are known carriers of a genetic mutation that causes a disease such as cystic fibrosis, Tay-Sachs disease or another single-gene disorder.

 The mother has a male relative with muscular dystrophy, hemophilia or some other X-linked disorder.

Accuracy and limitations of the test Although amniocentesis is accurate in identifying certain genetic disorders, it can’t identify all birth defects. For example, it can’t detect a heart defect, autism, or cleft lip and palate. A normal result from an amniocentesis may provide reassurance regarding certain congenital problems, but it doesn’t guarantee that your baby is free of all defects.

Chorionic villus sampling Like amniocentesis, chorionic villus sampling (CVS) can detect chromosomal and other genetic abnormalities in your unborn baby. However, instead of sampling amniotic fluid, CVS examines tissue from the placenta. Part of the placenta is made up of a membrane layer called the chorion. Tiny, hair-like projections called villi extend out of the chorion and act as routes for nutrients, oxygen and antibodies from you to your baby. These chorionic villi contain fetal cells complete with your baby’s chromosomes and DNA.

When and how it’s done CVS is usually performed between the 9th and 14th weeks of gestation, earlier than amniocentesis is typically done. If you wish to have a diagnostic test early in your pregnancy, your doctor may recommend CVS because of the increased risk of complications that early amniocentesis carries.

During the procedure, your doctor takes a sample of chorionic villus cells from the placenta by inserting a thin, hollow tube (catheter) through your vagina and cervix or by inserting a needle through your abdomen. The sample is then sent to a laboratory for analysis. Both approaches (abdominal and cervical) are considered equally safe. Which approach your doctor uses depends on the position of the placenta and his or her experience. In general, placentas on the back side of the uterus are easier to sample through the cervix. Placentas in the front allow for either approach.

An ultrasound is done before the procedure to determine the position of the placenta, and ultrasound guidance is used throughout the procedure.

CVS requires more expertise than does amniocentesis, so it’s important to have an experienced obstetrician perform the procedure. In general, the risks of CVS are similar to, though slightly higher than, those of amniocentesis. They include miscarriage, post-procedural complications and Rh sensitization.

There was once some controversy about whether CVS causes an increased incidence of limb defects. Reports at that time showed a slight increase in limb malformations with CVS. Since then, other studies haven’t found any increase. The risk of limb defects appears to be a concern only if the procedure is done before the 9th week of pregnancy.

A vaginal speculum opens the vagina, and a catheter is inserted through the cervix into the chorionic villi during a transcervical chorionic villus sampling (CVS). A sample is gently removed by suction for testing in a laboratory. As with amniocentesis, the doctor uses an ultrasound image to check the position of the fetus and guide the catheter into position.

What the results may tell you As in amniocentesis, analysis of fetal cells in the sample can tell you whether your baby has a chromosomal abnormality, such as Down syndrome. In pregnancies at risk for specific genetic disorders, DNA obtained from CVS can be used to test for the specific disease. The advantage of CVS over amniocentesis is that results are available earlier in pregnancy.

Accuracy and limitations of the test CVS has less than a 1 percent chance of yielding false-positive results. A false-positive means that the test indicates the baby has an abnormality when there really is none. If you get negative results, you can be almost certain that no chromosomal abnormalities are present in your baby. But CVS can’t be used to check for all conditions. For example, it can’t be used to test for neural tube defects, such as spina bifida.

Percutaneous umbilical blood sampling With percutaneous umbilical blood sampling (PUBS), a sample of blood is taken from your baby through the vein of the umbilical cord. This diagnostic procedure can detect chromosomal abnormalities, some genetic problems and infectious disease. PUBS is also known as umbilical vein sampling, fetal blood sampling and cordocentesis.

Your care provider may offer this procedure if other diagnostic tests, such as amniocentesis, ultrasound and CVS, have been unable to provide sufficient information. In the past, PUBS offered the fastest way to gather a sample for chromosomal analysis, but new laboratory techniques, such as FISH, allow chromosomal evaluation to be completed more quickly and with less risk.

PUBS also may be performed to diagnose certain blood disorders and infections and to supply blood transfusions to the baby.

When and how it’s administered PUBS is usually done later in the pregnancy, after 18 weeks. Before this point, the umbilical vein is still fragile and the procedure is much more difficult. Similar to an amniocentesis, you lie on your back with your abdomen exposed. Gel is spread over your abdomen, and advanced ultrasound is used to locate the umbilical cord. Your doctor inserts a thin needle through your abdomen and uterus into the umbilical cord vein and withdraws a sample of blood. The sample is then sent to the laboratory for analysis. Your baby will likely be monitored for a short period after the procedure to make sure that the baby is doing well.

PUBS carries a higher risk of miscarriage — about 1 to 2 percent — than that of CVS or amniocentesis. Other risks associated include bleeding from the needle entry site, which usually goes away on its own, temporary slowing of the baby’s heart rate, infection, cramping and fluid leakage.

What the results may tell you PUBS can identify chromosomal disorders, but is rarely the first choice for this purpose. More often, PUBS may be used to determine blood disorders and infections.

Because PUBS is somewhat riskier than other prenatal tests, your care provider will probably offer you other diagnostic options before PUBS. But if you’re Rh negative, your baby is Rh positive and Doppler ultrasound indicates your baby has significant anemia, PUBS can be used to determine whether the baby requires a transfusion.

Having an experienced care provider perform the procedure is critical to the test’s success.

SPEEDING UP TEST RESULTS

One of the downsides of traditional genetic analysis is that it can take days to weeks to get the results because lab technicians must wait for sample cells to divide and multiply (culture).

A faster method of genetic analysis is called fluorescence in situ hybridization (FISH). It can deliver results in as little as 24 to 48 hours. FISH uses a technique that relies on short sequences of DNA called probes. These probes, which have a fluorescent tag attached to them, are designed to seek out and attach (hybridize) to specific genetic sequences in a cell sample. When the sample is viewed under a fluorescent microscope, the tags are easy to see and count. Culturing isn’t needed, which allows for much faster evaluation.

FISH is generally very accurate. It has false-positive and false-negative rates of less than 1 percent. But the technique has some limitations. Some structural abnormalities, which can indicate a problem, aren’t evident with FISH. In addition, FISH can’t tell differentiate between maternal cells and fetal cells. As a result, doctors tend to use FISH as a supplemental test, not as the sole basis for prenatal decisions.

On the horizon As DNA analysis continues to evolve, newer and less invasive tests will likely become more widely used. One example is a technology called array-based comparative genomic hybridization (aCGH). Unlike FISH, which is used to examine a specific genetic target, aCGH technology examines a person’s DNA at multiple sites for many different genetic disorders. Another type of test is prenatal testing of free fetal DNA (ffDNA). In contrast to chorionic villi sampling and amniocentesis, it uses fetal genetic material extracted from the mother’s blood and, therefore, is noninvasive. Recent studies indicate ffDNA testing can be used to determine if a fetus has Down syndrome, and possibly other genetic problems. This type of testing is still very expensive and in need of additional research, but it appears to be more accurate than current screening methods for Down syndrome.

LATE PREGNANCY TESTS

Under certain circumstances, your care provider may recommend tests to check on your baby’s health late in your pregnancy. These include electronic fetal nonstress and stress tests, biophysical profile testing and Doppler ultrasound.

Fetal nonstress and stress tests

The fetal nonstress test is a simple, non-invasive test. The test is named nonstress because no stress is placed on the fetus during the test.

During this test, baby’s movement, heart rate and heart rate reactivity to movement are measured for about 20 to 30 minutes. If the baby doesn’t move, it doesn’t necessarily indicate there’s a problem; the baby may just be asleep. A non-reactive test can indicate if the baby isn’t receiving enough oxygen because of placental or umbilical cord problems.

For a fetal contractions stress test, the hormone oxytocin is given to you intravenously (by IV) to cause labor contractions. In some cases, you may be asked to massage your nipples. This tells your body to release oxytocin. If your baby’s heart rate slows down (decelerates) in a certain pattern after a contraction, your baby may not be receiving adequate oxygen and may not tolerate labor and delivery.

Your care provider may recommend a nonstress test or a contractions stress test if you notice a marked decrease in your baby’s movement, you have a medical complication or if your baby’s growth rate seems abnormally slow.

When and how they’re done These tests are generally performed after pregnancy has reached at least 28 weeks. They’re performed as follows:

 Nonstress test. For this test, a transducer that measures your baby’s heart rate and a monitor that records fetal movements and uterine contractions are attached to your abdomen. Your provider will look for changes in baby’s heart rate pattern over time. Most of these changes occur in association with your baby’s movement.

 Contraction stress test. The contraction stress test is performed in much the same manner as the nonstress test, but baby’s fetal heart rate is measured while you’re having mild contractions. The contractions may have to be induced.

What the results may tell you Results are abnormal when the baby’s heart rate doesn’t accelerate as expected. As scary as this may sound, an abnormal result may not mean that your baby is in danger. The test has a high false-positive rate, suggesting there’s a problem when there really isn’t one.

Reasons to have it done In addition to a decrease in movement, your care provider may suggest undergoing a nonstress test if you have one of the following conditions:

 Diabetes

 Kidney or heart disease

 High blood pressure

 A history of stillbirth

 You’re past your due date

 You’re carrying two or more babies

Accuracy and limitations of the test Both tests have very high false-positive rates. A false-positive means the test indicates a problem when there actually is none. However, results indicating that baby is healthy are quite reliable.

Biophysical profile testing Biophysical profile testing combines an ultrasound examination with a nonstress test. The tests generally assess five different aspects of your baby’s health, including his or her:

 Heart rate

 Breathing movements

 Body movement

 Muscle tone

 Amniotic fluid level

Each of these factors is given a score of 0 or 2, and the scores are added together to achieve a total from 0 to 10. Biophysical profile testing helps you and your care provider keep track of your baby’s health before delivery, particularly if you have a high-risk pregnancy.

When and how it’s done This test may be used as early as the 26th week of pregnancy, but it more typically is started at 32 weeks of gestation.

Your baby’s heart rate is measured using a nonstress test. The other four factors — breathing, movement, muscle tone and amniotic fluid — are evaluated with ultrasound. If a factor is normal, it receives an individual score of 2. If it’s absent or less than expected, it receives a score of 0. (All scores are even numbers.)

What the results may tell you A score of 6 or less may indicate your baby is suffering from a lack of oxygen. The lower the score, the greater the cause for concern. Depending on the baby’s age and the circumstances, your care provider may recommend delivery.

Accuracy and limitations of the test The false-positive rate for any individual factor of the biophysical profile is high, but when all factors are combined, the false-positive rate decreases. Having a low score doesn’t necessarily mean that your baby must be delivered. It may just mean that you need special care throughout the rest of your pregnancy.

Doppler ultrasound Doppler ultrasound is another method to evaluate your baby’s health late in pregnancy. It’s used to monitor blood flow through your baby’s blood vessels. Doppler testing may be used to determine where and how fast baby is distributing blood flow throughout its body and the placenta. Doppler studies are also used for babies at risk of fetal anemia, characterized by abnormally low levels of blood or red blood cells in baby’s bloodstream.

WHEN THE RESULTS INDICATE A PROBLEM

The unthinkable is happening: Your prenatal test results suggest that your baby has a problem. Amid the shock, worry and fear, one question surfaces: What do we do now?

Make an appointment with your care provider to talk about what the findings may or may not mean. Here are some questions you might consider asking your care provider during your appointment:

 How accurate are the test results? Is it possible there’s a mistake?

 Can my baby survive this condition? If so, how long is he or she likely to live after birth?

 What problems might be caused by this condition? How might the baby be affected physically? How might the baby be affected mentally?

 Are there additional tests that can provide more information about the baby’s condition?

 Is it likely that my child will need surgeries or other medical treatments to manage the condition?

 Are there other health care professionals who can give us more information?

 What is involved in caring for a child with this condition?

 Is there a support group in our community for families who have a child with this condition? How can we contact parents of children who have a similar condition?

 What are the chances that this condition will affect our next pregnancy?

 What resources are available to us if we decide to end the pregnancy? What counseling services or support groups are available?

The information you gather can help you make decisions based on your personal circumstances.



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