In early pregnancy, this procedure is done in the 15th to 18th week to asses the inherited or age-related disorders that may affect the fetus. Over the age of 35 and particularly over the age of 40, women have a higher chance of giving birth to a child with Down’s syndrome. In late pregnancy, this procedure is reserved for instances where there are complications such as bleeding, premature labor, or anything that might indicate the need for earlier-than-term delivery. In this case, a small amount of amniotic fluid is withdrawn and tested for the ratio between concentrations of lecithin and sphingomyelin. L/S ratios, which are phospholipids useful in predicting fetal lung maturity, which in late pregnancy, is an important, factor in determining fetal viability in a preterm delivery. Fluid can also be evaluated for infection, karyotyping ,and fetal sex.
After the abdominal area is cleansed with a surgical soap, a needle is guided through the abdomen in an area that has already been locally anesthetized. With the guidance of ultrasound images, the needle is inserted through the uterine wall and into the amniotic sac. A small amount of fluid is then withdrawn and sent for testing. Results usually take two to three weeks for genetic and alpha-FP testing and a few hours for L/S ratios. In both instances, they are nearly 100% accurate.
The risks involved in an amniocentesis include a risk of bleeding and a risk of miscarriage and Rh-isoimmunization. This latter risk is usually around 1 to 2%. If minute amounts of fetal blood escape into the maternal circulation in a pregnancy where there is Rh incompatibility, Rh sensitization may occur. For this reason, all Rh-negative mothers who undergo this procedure are vaccinated with Rh immune globulin immediately after the amniocentesis and again at 28 weeks to prevent the formation of antibodies.
CHORIONIC VILLUS SAMPLING
This procedure the examiner takes a sample of the fetal tissue in early pregnancy (8 to 12 weeks) which is destined to form the placenta and sends it for genetic testing. This tissue, known as the chorionic villi, surrounds the entire fetal sac. The advantage is that results can be obtained very early in the pregnancy so that pregnancy termination, if so desired, can be done earlier and easier. Another advantage is that the amniotic sac is not invaded.
After appropriate cleansing with surgical soap, a needle is inserted through the cervix or through the abdominal wall to obtain a sample of chorionic villi. As with the amniocentesis, a local anesthetic and ultrasound guidance are used.
Ultrasound is generally considered risk-free. There has been no evidence of harm to the fetus.
NONSTRESS TEST (NST)
This test uses no-evasive monitoring to evaluate for fetal stress caused by conditions such as aging placenta, maternal illness like diabetes and malnutrition.
This test is usually done in the labor suite or in your doctor’s office. An external ultrasound monitor is strapped to your abdomen over the fetal heartbeat area. The fetal heartbeat is recorded on a monitoring strip of paper. Every time you feel fetal activity, you will push a hand held button to place a mark on the monitoring strip. If the heart rate rises with fetal movement, the test is classified as reactive. If there is no increase in heart rate with movement, the test is non-reactive and may indicate fetal stress. The test usually takes 30 minutes or so and is repeated every few days or every week as long as it is indicated.
There is no risk to this procedure.
FETAL STRESS TEST
This test is reserved for those with no reactive non-stress tests and serves to uncover a nutrient or oxygen supply problem that may exist in the fetal environment.
To create stress, an intravenous infusion of oxytocin is started which produces mild uterine contractions. Monitors are placed on your abdomen to measure both the fetal heart rate and the intensity and frequency of the contractions. Under normal circumstances, the uterine contractions should not alter the fetal heart rate, however, if there is a problem, there will be a change in the heart rate with the contractions. The test results are then classified as positive.
Since the uterine contractions can be monitored and swiftly stopped or reduced by cutting off the infusion of oxytocin, this test is considered safe. Rarely does it precipitate any dangerous fetal distress, and if it does, it generally occurs in a pregnancy where fetal stress is already extremely high.
BREAST STIMULATION TEST
This test achieves the same results as the fetal stress test, only instead of using an intravenous infusion of oxytocin, breast stimulation is done to produce a natural oxytocic substance in the maternal circulation. This is considered safer and less invasive but is relatively unpopular in those who regards breast manipulation as a form of sexual fondling or abuse.
This is a test that utilizes a flexible fiber optically lit fetoscope to directly visualize the fetus sometimes after the 16th week. It is inserted through the mother’s cervix or abdomen into the womb. Ultrasound is used for guidance purposes. A grasping device can be used to take biopsies of fetal tissues and samples of fetal and placental blood. Some centers can even perform fetal surgery through fetoscope Progress in this field has been slow, because the risk-benefit ratio is under considerable scrutiny.
Maternal risks are slight. Infection may occur but is not common. The fetal risk consists of a 3 to 5% chance of premature labor and its inherent dangers, including death.