Prenatal Tests to Consider

regnancy is incredibly exciting, but it's also a bit scary. As the reality of having a baby sets in, it's hard not to worry about whether your baby will be healthy. In the old days, doctors simply told women not to think about it.

Modern women think a lot about such things. Today's expectant mothers are much better informed than were their own mothers, and have heard about many of the more than 3,000 congenital disorders parents can pass along to their babies. Fortunately, there are now several prenatal tests that can help reassure the majority of expectant parents that their babies are just fine. And when there is a possible problem, these tests give the couple time to go through counseling and make an informed decision about continuing the pregnancy.

In addition to all the high-technology techniques generally available to pregnant women in the 1990s, there are many routine prenatal procedures that have been keeping babies safe for decades. Certain common laboratory tests are repeated every time you see your doctor; others are done periodically throughout the pregnancy.

Routine Tests

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During your first prenatal appointment your doctor will determine your blood type and test for anemia, exposure to such sexually transmitted diseases as syphilis and AIDS, and perhaps for signs of drug abuse. He or she will also examine your vaginal secretions for the presence of gonorrhea, which can cause potentially serious eye infections if transmitted to a baby during birth.

You will also have a Pap smear to rule out possible cancer of the cervix and a urine test to detect the presence of bacteria that could indicate a current or potential infection. Your doctor also needs to know whether you have ever been exposed to rubella (German measles). This childhood disease can produce severe birth defects if contracted during pregnancy. This initial battery of tests gives the physician a fairly good idea of your overall health.

Certain tests must be repeated at every prenatal visit to make sure you—and your baby—stay healthy. Your blood pressure will be checked regularly. Your doctor will also examine your urine. Too much sugar in the urine could mean you are developing gestational diabetes; too much protein could indicate the danger of toxemia.

In the fourth month of pregnancy, the doctor will probably check your blood again for anemia. In the sixth month of pregnancy, he or she will take a specimen from the cervix to test for the presence of group B streptococcus. If these bacteria are present, you may be treated as soon as labor starts in order to keep the baby from becoming infected during birth.

Later at 28 weeks, you will probably have a glucose tolerance test to check for diabetes. Women who are already diabetic will need this test earlier and will probably have it done more than once.

At the beginning of a glucose tolerance test, a small amount of your blood is drawn and examined to determine how much sugar is present. Following this you will drink a fruit-flavored preparation with a high concentration of glucose. Then blood will be drawn at various intervals and tested to determine how well your body is able to handle—and get rid of—all this extra sugar.

Any further testing depends on your medical and family history and that of the father, as well as the course of your pregnancy. Despite the fears common to all parents that something could be wrong with their baby, the incidence of chromosomal and other congenital defects has been greatly reduced by the common use of such procedures as amniocentesis, ultrasound, chorionic villi sampling, and alpha-fetoprotein screens.

Ultrasound

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The advent of ultrasonography gave physicians a safe way of examining a developing baby without the risk of invading the womb or disturbing the pregnancy. Ultrasound uses sound waves bouncing off the baby—and anything else in the womb—to create a picture of the pregnancy without the potentially harmful effects often associated with x-rays.

The procedure is now used routinely to date a pregnancy, since it allows the doctor to see whether the size of the baby corresponds with the reported length of time since conception. Ultrasound also helps physicians monitor the baby's growth during the pregnancy if there is any concern that the baby is too small or too large.

Ultrasound is helpful in confirming or ruling out pregnancy; determining the presence of more than one baby; assessing the development, health, and location of the placenta; and checking the volume of amniotic fluid in the uterus.

These sound-wave pictures also help physicians look for suspected congenital abnormalities. With ultrasound, doctors are actually able to see the baby's organs and central nervous system and look at the baby's bones to make sure the skull, arms and legs are the right size for its prenatal age.

Your doctor will order an ultrasound if he or she cannot hear a heartbeat, if the baby isn't moving or there is a change in the pattern of movement. The doctor will also want to take a look at the placenta when there is any bleeding—especially if the bleeding occurs early or late in the pregnancy.

As the time of delivery nears, ultrasound helps physicians determine the baby's position (presentation) and identify any potential problems that might interfere with birth. If a baby has to be delivered early, ultrasound helps ensure that it is mature enough to survive. If the infant seems to be overdue, the doctor can use ultrasound to check on its size.

Ultrasound has greatly improved the safety of other diagnostic procedures such as amniocentesis and chorionic villi sampling. Indeed, without the road map the ultrasound picture provides, many physicians and parents would probably consider the risk of such testing far too great.

Ultrasound is a simple, quick procedure. The physician either inserts a probe into the vagina or moves what is called a transducer back and forth across the abdomen. Either way, the instrument records the echoes of sound waves bouncing off anything encountered in the uterus. These echoes make pictures that are shown on a sort of television screen attached to the unit.

The single biggest drawback is that women who are having an abdominal ultrasound must drink a lot of water beforehand and aren't allowed to go to the bathroom until after the examination. Any woman who has ever been pregnant knows just how uncomfortable a really full bladder can be.

Apart from all the medical benefits of ultrasound, prospective parents also have the thrill of actually seeing their baby months before he or she arrives. Those grainy pictures do much to make up for all the aches and pains of the first few months of pregnancy. The pictures also kick-start the parent-child bonding that, in the old days, didn't begin until well after delivery.

Amniocentesis

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Amniocentesis is the granddaddy of modern prenatal testing. This procedure has been available to expectant mothers for some 30 years and has now become routine for the increasing number of pregnant women over 35, when the chance of problems with the baby goes up.

Doctors recommend amniocentesis when either parent or a previous child has a chromosome abnormality, when either parent is a carrier for certain disorders, when an earlier child was born with a neural tube defect such as spina bifida (a partially open spinal column), or when there is a family history of such chromosomal disorders as Down syndrome.

Physicians also suggest amniocentesis if the mother has a history of miscarriage. Another potential reason is the presence of too much alpha-fetoprotein in the mother's blood. This substance is produced by the baby, and an excessive amount could indicate a potentially serious problem with the pregnancy.

During the pregnancy, the baby floats in a liquid called amniotic fluid. As the baby matures, cells from his or her body are discarded into the fluid. Amniocentesis enables physicians to retrieve these cells and study the genetic information they contain. The presence—or absence—of certain chemicals in the fluid also helps doctors determine how well the baby is doing.

Amniocentesis is generally performed during the 16th or 17th week of pregnancy. The procedure can be done any time from week 14 through week 20. Before week 12, it's unlikely that the body has produced enough amniotic fluid for a good specimen. The problem with waiting until the 19th or 20th week is that the mother will be in her fifth month by the time the test results are available, and the longer you wait, the more difficult it is to perform a therapeutic abortion should the couple decide to terminate the pregnancy. Amniocentesis is sometimes done toward the end of the pregnancy to see whether the baby's lungs are mature enough to allow him or her to breathe independently in case of premature labor or the need for an early delivery due to a medical problem.

AMNIOCENTESIS: WEIGHING THE RISKS

If there's a danger that the baby will be born with a congenital defect, your doctor will probably recommend amniocentesis to rule the problem out. This test requires a sample of the baby's cells, which are always present in the surrounding amniotic fluid. Collecting the sample is not without risk, since the doctor must insert a needle directly into the uterus. However, the odds of a mishap are extremely low. When done in the 16th week of pregnancy, only 1 in 200 procedures results in loss of the baby.

During amniocentesis, you recline on a table and are hooked up to an ultrasound machine. First the position of the baby and placenta are located by ultrasound. The doctor will then swab your abdomen with an antiseptic and insert a long thin needle into your uterus. There is a burning or stinging sensation and a feeling of pressure as the physician maneuvers the needle to obtain a small amount of amniotic fluid. (Some physicians give their patients a local anesthetic; others do not, since the anesthetic needle causes about the same amount of discomfort as the other one.)

Ultrasound is a very important part of the amniocentesis procedure. It helps the doctor locate the placenta and keep the needle far away from the baby when taking the specimen, thus avoiding potential complications.

There is a slight risk that amniocentesis will trigger premature labor or that the mother could develop an infection. In rare cases, there may be a little bit of vaginal bleeding or some loss of amniotic fluid. Most women, however, merely have some mild cramping—if anything—and are able to resume their normal routine soon after the procedure.

The amniotic fluid specimen is sent to a special laboratory that performs genetic studies. The fluid is cultured in a laboratory dish, and the cells are allowed to grow. The cells are then examined for any chromosomal abnormalities.

Test results are generally available within 1 to 2 weeks. Most prospective parents learn that all is well and are then able to enjoy the final months of the pregnancy. When the studies indicate a possible problem with the baby, the couple still has enough time to carefully consider the difficult choice that confronts them.

Although amniocentesis cannot diagnose such sex-linked disorders as hemophilia or muscular dystrophy—which occur only in males—the test can determine the sex of the baby. If the baby is a girl, the parents need not worry. If the baby is a boy, there is a 50-50 chance that the child will be affected if the mother carries the gene for the disease.

Chorionic Villus Sampling

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The chorionic villi are slender projections attached to the chorion, a membrane which eventually becomes the part of the placenta closest to the baby. Since this membrane begins to develop as the result of fertilization, the material contained within the chorion—and the chorionic villi—accurately reflects the baby's genetic recipe. Physicians can test a sample of this material for a wide range of congenital conditions.

Chorionic villi sampling offers a big advantage over amniocentesis because it can be done as early as the eighth week of the pregnancy. Test results are generally completed within two weeks. Therefore, the pregnancy can be terminated if necessary, early in the second trimester—or even within the first trimester—when a therapeutic abortion is most safely performed. The relatively early diagnosis also allows couples to make this difficult decision in private, before the pregnancy is apparent to family and friends.

The procedure is currently performed in a hospital, generally between weeks 9 and 12 of the pregnancy. The sample is obtained by snipping or suctioning the tiny, finger-like villi.

As with amniocentesis, ultrasound monitoring establishes the whereabouts of the fetus and the placenta. The area of entry is swabbed with an antiseptic agent to prevent infection. The physician then inserts a needle either through the vagina and the cervix, or through a small incision in the abdomen. The needle is maneuvered into place following the map provided by the ultrasound. The doctor will pump the needle several times to obtain a sufficient sampling of chorionic villi.

Results for tests that do not require the cells to be grown in a culture are usually ready in a day or two. Tests that do require a cell culture may take up to two weeks to complete.

Many women experience emotional and physical fatigue following this procedure. There also may be some bleeding. The bleeding is not a cause for concern unless it lasts longer than two days. The risk of miscarriage is about the same as that associated with amniocentesis. However, many couples having this test believe that the benefit of a much earlier diagnosis far outweighs the still-slight risk of a miscarriage. (There is still some debate over the possibility that this test may sometimes cause deformities.)

FOR EARLIER TEST RESULTS: CHORIONIC VILLUS SAMPLING

This relatively new test allows your doctor to detect a congenital defect in the baby as early as 8 weeks into the pregnancy. The genetic content of the chorion, a membrane in the placenta, parallels that of the baby itself. To obtain as sample, some of the tiny villi that line the chorion are sucked out through a narrow tube advanced into the uterus through the cervix and vagina, or directly into a needle inserted through the abdomen. Risks involved in this procedure are comparable to those of amniocentesis: in approximately 1 in 200 cases, the baby is lost.

Alpha-Fetoprotein

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Alpha-fetoprotein (AFP) is a type of protein produced only by a fetus or the fetal yolk sac. The mother-to-be does not produce this substance on her own. Screening for AFP involves analyzing the level of the protein in the mother's blood. The test is generally performed between the 16th and 18th weeks of pregnancy.

An excessive amount of AFP in your blood could indicate that the baby has a neural tube defect such as the spinal deformity known as spina bifida. There could also be a high AFP reading if more than one fetus is producing the alpha-fetoprotein. An elevated level may also indicate that the pregnancy is more advanced than the initial estimate. An abnormally low amount of AFP may point to the possibility of Down syndrome or another chromosomal problem.

It is important to remember that this is only a screening test. It is not a diagnostic procedure. AFP testing will not tell you for sure that something is wrong, but rather that the matter should be pursued further. For example, if a second AFP test also showed low AFP levels, you would be advised to have amniocentesis to rule out the possibility of Down syndrome.

The AFP test itself is safe. However, if the test falsely indicates that there may be a problem when everything is really fine, mother and baby could then be exposed to the unnecessary risk of a more invasive procedure.

The statistics associated with this screening test are overwhelmingly on the side of a normal baby. Before subjecting that baby to any unnecessary risk, it's essential to obtain a second test—and perhaps a second opinion—from physicians experienced in genetic testing. There are still other studies to expect late in the pregnancy. Your doctor may ask you to lie quietly for an hour and count the number of times your baby moves to make sure the child is active enough. A sluggish baby may already be a baby in trouble. If there is concern about the baby's heart rate, you will be hooked up to a special fetal monitor that traces each heartbeat.

If there is any reason to believe that the baby is at risk during the last month of the pregnancy—or if the baby is overdue—you will have what is called a “non-stress” test. Your doctor will have you lie on a table while a fetal monitor records the baby's heartbeat in relation to its activity. This record allows physicians to see exactly how well the baby is doing.

If a baby's performance is worrisome, the doctor may order a stress test. In this procedure, you are given a small amount of oxytocin, the drug used to induce labor when the contractions don't start on their own. The doctor will then use ultrasound to see how well the baby will be able to handle the demands of labor and delivery. The major drawback is that the oxytocin could start actual labor. That's why such testing is performed in a hospital near the labor and delivery suites.

Many other prenatal tests are currently being studied and will no doubt be commonplace someday. Indeed, it really hasn't been that long since AFP screens and chorionic villi sampling were brand new procedures. As each new test becomes available, your odds of having a healthy baby should continue to improve.