Prenatal Testing at the Perinatal Center
Last updated: 03/09/2009
Nuchal Translucency Screening
The first trimester nuchal translucency screening determines the woman's risk for her baby to have chromosomal abnormalities. The most common of these include Down Syndrome (Trisomy 21), Trisomy 18, Trisomy 13 and sex chromosome abnormalities such as Turner Syndrome or Kleinfelter Syndrome. Some of these abnormalities cause birth defects and mental retardation. This test can be performed between 11 and 13 weeks into the pregnancy. The ultrasound measures the amount of fluid accumulated within the skin behind the fetus' neck.
Chorionic Villus Sampling
If there are ultrasound abnormalities found in a fetus, further testing can be performed using Chorionic Villus Sampling, which will give the definitive chromosomal diagnosis. CVS can be done either through a catheter vaginally or by needle abdominally. The procedure has a one percent risk for miscarriage. Preliminary results are available within three to five working days and the final report is available in two weeks.
The CVS test is followed by a full anatomy survey by ultrasound at 9 to 11 weeks of gestation, which can rule out more than 80 percent of abnormalities.
Ultrasound
Ultrasound can pick up genetic markers for Down Syndrome and other chromosomal problems in the second trimester. The markers that ultrasonographers look for include cysts in the blood vessels of the fetus' brain, major structural defects including heart defects, long bones that are shorter than they should be, dilation of the fetus' kidneys, a missing bone in pinky fingers, bright spot in the heart chamber and bowel and sandal gap toes among others. Further testing can be done by amniocentesis.
Amniocentesis
Amniocentesis is a 15- to 30-minute procedure in which a needle is inserted into the uterus to take a sample of the fluid surrounding the fetus. It is an elective procedure that may be chosen by women with certain risk factors. The patient is numbed, and the physician uses ultrasound as a guide for inserting the needle through the abdomen. The equivalent of about two tablespoons of fluid around the baby is removed and sent for chromosomal and biochemical analysis. With amniocentesis comes the risk that one woman in every 200 may have a miscarriage because of the procedure.
Other Tests
Other evaluation measures to follow high-risk fetuses include weekly biophysical profiles by ultrasound, non-stress fetal heart rate monitoring and Doppler studies. Biophysical profiles are performed to observe fetal behavior such as fetal movement, tone, breathing and amniotic fluid volume. Umbilical artery Doppler ultrasound is used to follow intrauterine fetal growth, and the middle cerebral artery Doppler flow is measured to monitor fetal anemia due to Rh incompatibility. Fetal blood transfusions can also be performed to help the fetus with Rh blood incompatibilities, which can lead to fetal anemia.
While the tests raise very serious questions for patients, a well-informed patient can then make intelligent decisions about her pregnancy. The center also provides genetic counseling for patients who receive news that they are of increased or high risk for having a child with a serious or ultimately fatal condition.
In some cases, the question is not whether to continue the pregnancy, but it may involve delivering the baby early or even performing minimal fetal treatment in utero to buy time until the fetus is capable of independent existence outside the womb and more definitive treatment can then be done by a pediatric surgeon.
Birth defects occur in one out of every 28 pregnancies, according to the March of Dimes. The decision to have prenatal screening is a personal one that should be made between the mother and her physician. If you are pregnant and interested in the newer, less invasive tests that are now available, call the Perinatal Center for more information at (304) 526-2124.