Prenatal Genetic Screening
Nuchal Translucency Screening: For many years, we have been offering a first trimester test which calculates the risk of the fetus having extra chromosomes, called trisomies. This test uses blood work from the mother, an ultrasound measuring the thickness of the baby’s neck and the mother’s age to perform a statistical analysis to give a likelihood of genetic abnormalities. The screening test has a 90-93% detection rate of Down Syndrome (Trisomy 21) and a 5% false positive rate.
Cell-Free Fetal DNA Screening: Tests are now available that can isolate fetal DNA from the developing placenta. These cells can be normally found in maternal blood after 10 weeks gestation. These new tests have a Down Syndrome detection rate of 99.1%. The American College of Obstetrics and Gynecology issued a statement in 2015 recommending that cell-free screening continue to be offered only to high risk women. We do not recommend this test for low risk women. Insurance companies may or may not cover this testing. For some patients this may result in bills of greater than a thousand dollars.
Gender Identification: Some of these tests have the added bonus of allowing you to find out the gender of your baby earlier. These tests, however, are not designed for that purpose but for finding abnormalities in the sex chromosomes. Our office does not do gender only testing.
If you do not want to know about chromosomal abnormalities but do want to know the gender early, at home tests that use the same technology are available. These look solely for gender and are less expensive. Like the other testing, it is >90% accurate but still has a rate of false results.
Amniocentesis (taking fluid from the sac surrounding the baby) and chorionic villus sampling (taking a small portion of the placenta) are more invasive and allow for growth of fetal cells outside of the pregnancy to see the chromosomes more completely. These tests are available to high risk patients, carriers of known genetic abnormalities, and those for whom screening tests are positive. These tests have a low yet present risk of pregnancy loss and are performed in consultation with the high risk obstetrician.