Tests Used In Pregnancy

Various tests and procedures are used in certain cases of pregnancy complications. Like all medical procedures, they offer advantages, but also carry risks. Therefore, they should be utilized only when medically indicated, not on a routine basis for you or your doctor’s convenience or to satisfy your curiosity.

When deciding whether to undergo a test, ask your caregiver if the results will in any way alter his care of you. If his answer is yes, ask him how. If his answer is no, ask him if the test is therefore necessary. Make sure you understand all the risks and benefits involved before agreeing to, or rejecting, a procedure. Continue to ask questions and to request explanations until you feel comfortable. Understanding the benefits can help to relax you and may free you from concern about the procedure. Or, it can help you decide to ask for an alternative.

Among the more common tests used in pregnancy are amniocentesis, chronic villus sampling, alpha-fetoprotein screening, ultrasound, X-ray pelvimetry, the estriol excretion study, fetal movement evaluation, the non-stress test, and the oxytocin challenge test.

Amniocentesis

Amniocentesis is a test to detect abnormalities in the baby. It may also be done to assess fetal lung maturity if induction of labor or cesarean delivery is indicated. The test is performed by administering a local anesthetic, then withdrawing a sample of amniotic fluid using a log needle inserted through the abdominal ad uterine walls. It should be done in conjunction with ultrasound, which will show the location of the fetus, the placenta, and the umbilical cord.

The amniotic fluid is sent to a lab for culturing and testing. Certain tests—such as those for Tay-Sachs disease, Hunter’s syndrome, neural tube defects, and fetal lung maturity—can be performed immediately. These tests measure chemicals produced by the baby that are present in the amniotic fluid. To determine fetal lung maturity, the amniotic fluid is examined for the specific phospholipids that are present when a baby’s lungs are mature.

Most tests require that the fetal cells be isolated and given sufficient time to multiply, usually 2 to 4 weeks. Then a complete chromosomal analysis is done to detect the presence of Down syndrome or other genetic abnormalities. The sex of the baby is also established.

When amniocentesis is used for detecting abnormalities, it is generally performed between 16 and 18 weeks gestation. Before 14 weeks, there usually is insufficient amniotic fluid. Some caregivers are performing amniocentesis between 11 and 13 weeks. But one study found that when amniocentesis is performed before 86 days, an increase in foot deformities (turned-in and club feet) was observed. When testing for gestational maturity, the procedure is done in the last trimester.

Amniocentesis is a very valuable procedure, but according to many experts, it can be misused. The risks include some chance of blood exchange between the woman and baby, creating a greater Rh incompatibility while testing for the condition; infection of the amniotic fluid; peritonitis; blood clots; placental hemorrhage; injury to the baby; and even premature labor. Amniocentesis should definitely not be done just to satisfy curiosity about the baby’s sex. And, unless you plan to terminate your pregnancy if an abnormality is found, or unless your doctor plans to alter your care, it is questionable whether you should have this test done just for the genetic information.

Chorionic Villus Sampling

Chorionic villus sampling (CVS) is a test that can detect genetic abnormalities earlier than amniocentesis can. It is usually done between the ninth and eleventh weeks of pregnancy. However, it is not available in all locations.

A chorionic villus is one of the fingerlike projections covering the developing embryo. It contains cells that have the same genetic composition as the embryo. In CVS, a sample of chorionic tissue about the size of a grain of cooked rice is removed. In one method, a suction catheter is inserted into the uterus through the cervix under the visual guidance of ultrasound. In another method, a needle is inserted into the uterus through the abdominal wall. Both methods take about a half-hour to complete.

The advantages of CVS are that it can be performed early in pregnancy and that results can be obtained more quickly than with amniocentesis. Up to 3 or 4 weeks may pass before amniocentesis results are known. The possible risks of CVS include infection, Rh sensitization, bleeding by the woman or baby, miscarriage, birth defects, and perforation of the fetal membrane. In addition, studies in England have indicated that fetal limb deformities may result from CVS, especially when it is done early in the pregnancy (before 66 days). Several American studies have failed to confirm this finding, however.

Alpha- Fetoprotein Screening

Alpha-fetoprotein (AFP) screening is a blood test done on the woman between the fifteenth and eighteenth weeks of pregnancy to screen for fetal abnormalities. AFP is a protein produced by the baby. A high level of AFP in the woman’s blood indicates a possible open neural tube defect, such as spina bifid or anencephaly. A high level may also be caused by a multiple pregnancy or a miscalculation of gestational age. A low level may indicate Down syndrome. Also measuring two other substances—human chorionic gonadotropin and unconjugated estriol—increases the accuracy of detecting Down syndrome. identifying about 70 percent of Down syndrome cases.

AFP testing has a history of false positive readings, however, and further testing should be done if the results are abnormal. The additional tests could include another AFP blood test, ultrasound for accurate determination of gestational age, or amniocentesis for a more accurate diagnosis.

Ultrasound

Ultrasound was developed during World War I when high-frequency sound waves were used to detect enemy submarines. A form of ultrasound used in pregnancy testing is the sonogram, which uses intermittent sound waves. The sound waves are directed intros the woman’s abdomen with an outline of the baby, placenta, and other structures involved in the pregnancy transmitted to a video screen. A sonogram is often used to determine fatal position, to estimate the maturity of the baby, or to confirm a multiple pregnancy. In addition, the location of the placenta can be pinpointed when placenta previa (low implanted placenta) is suspected. Ultrasound is also used to visualize the baby and placenta when amniocentesis or CVS is being performed. since X-rays are now considered dangerous to developing babies, ultrasound is used instead.

Many doctors use ultrasound routinely to determine the due date. When the test is performed between the fourteenth and twentieth weeks, it is accurate to within 1 week before or after the estimated date. Later in pregnancy, and especially after the thirty-second week, it is not as accurate at determining due date because of variations in fetal growth. In a higher-risk pregnancy, an accurate due date is important for making sure that the infant is delivered at the best time. Routine ultrasound is usually done between the sixteenth and nineteenth weeks of pregnancy.

Ultrasound can also be directed in a continuous wave to check the baby’s heart rate. This is done during routine examinations using a doptone. Most often, it is done during labor using an electronic fetal monitor.

Ultrasound can also be used to measure the biophysical profile of a fetus. This type of profile includes fetal movements, muscle tone, amount of amniotic fluid, and fetal breathing movements. The test is usually done in higher-risk pregnancies to assure fetal well-being and to determine the best time for delivery.

Diagnostically, ultrasound is preferred over X-rays. However, many doctors now use ultrasound routinely during labor, as well as recommending one or more sonograms during pregnancy. The same as other procedures, ultrasound should not be used indiscriminately, and you have the legal right to refuse it. A 6-year study by the National Institute of Child Health and Human Development, a division of NIH, concluded that no benefit is derived from the routine use of ultrasound in low-risk pregnancies. This study, the largest ever conducted, found that perinatal outcome was not improved by routine screening when compared with the selective use of ultrasonography based on the caregiver’s judgement. The investigators estimated that $1 billion a year could be saved if sonograms are limited to higher-risk pregnancies and other cases in which it is medically indicated.

If your caregiver requests a sonogram and you do not have insurance to cover the cost, ask if the procedure is medically necessary and what information your caregiver hopes to receive. Also, ask if the information will change your care. In addition, if you are going to have a sonogram, you may want to ask about the credentials of the person performing and interpreting the test. Does that person have training or certification in ultrasonography? The FDA has guidelines regarding the intensity of the machines and the amount of time a fetus should be exposed.

Because so much information can be gained about the fetus through diagnostic ultrasound, and because studies have not shown any long-term effects on babies, many doctors feel strongly that the benefits of ultrasound outweigh the risks. Others, however, oppose its use without a medical indication, since routine screening of all women is still not recommended by the NIH or the American College of Obstetricians and Gynecologists.

X-Ray Pelvimetry

X-ray pelvimetry measures the size of the woman’s pelvis to determine if the passageway is adequate. It is seldom used except at the end of pregnancy when a breech presentation is suspected and the doctor needs to determine whether a vaginal delivery is possible. X-rays are avoided because they carry the risk of being carcinogenic (cancer producing).

Estriol Excretion Study

Estriol is an estrogen-type hormone made by the placenta and excreted in the woman’s blood and urine. The estriol excretion study measures the estriol level and helps to determine the functioning of the placenta, as well as the baby’s well-being. The test can be conducted using urine collected over a 24 hour period or a single sample of blood.

A drop in the estriol level indicates that the placenta’s functioning is declining. Several consecutive studies may need to be done to assess the degree of placental functioning.

The estriol excretion study is used, along with other tests, to determine the best time for delivery in cases of diabetes or other difficulties.

Fetal Movement Evaluation

Around the eighth month of your pregnancy, your caregiver may suggest that you keep track of your baby’s movements. You can do this best by setting aside a certain time each day and recording how long it takes your baby to move ten different times. A healthy baby moves about the same amount each day. Report any decrease in movement to your caregiver immediately. Fetal movement evaluation is a noninvasive test that cam provide valuable information about your baby’s health and well-being.

Nonstress test

A nonstress test can be a very reliable noninvasive test for fetal well-being. It is done by measuring the fetal heart rate in response to fetal activity as observed on a fetal monitor.

In a nonstress test, the woman is placed on an electronic fetal monitor and a baseline heart rate is noted. The woman is given a control to push when she feels the baby move. The control places a mark on the readout. Sometimes, a small transducer is used to make a buzzing sound over the baby’s head. When this is done, the test is called a vibroacoustic simulation test (VST).

An in crease in the fetal heart rate indicates fetal well-being. If the result is negative, additional testing, such as an oxytocin challenge test, is usually performed.

Nonstress test results can be affected by low blood sugar, so you should make sure to eat before taking the test. The results can also be affected by sleepiness of the fetus.

Oxytocin Challenge Test

The oxytocin challenge test ( OCT) is done in the hospital to help determine how well the baby will undergo the stress of labor. The OCT is also known as stress test.

Oxytocin is a medication that causes uterine contractions. While reclining at a 45-degree angle, the woman is given oxytocin intravenously until she has contractions 3 to 4 minutes apart for a full half-hour. At the same time, the baby’s heart rate is electronically monitored to check the effect of the contractions on him. If the results are positive—that is, the fetal heart rate appears abnormal during the stress of the contractions—the doctor may recommend a cesarean birth, since the baby may not be able to tolerate the stress of labor. If the results are negative—that is, the heart rate remains normal during the contractions—the baby will most likely do well during labor.

When taking the OCT, avoid lying flat on your back. This can cause your blood pressure to drop, decreasing oxygen to the baby and possibly causing the appearance of fetal distress on the monitor.

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