Your doctor may perform genetic testing to assess the baby’s risk of certain conditions if you are age 35 or older, or if you had another baby who was born with genetic irregularities. These tests also may be performed if an ultrasound scan indicates a birth defect such as a congenital heart defect. If tests indicate that the mother is a carrier for a genetic condition, the father’s blood may also be tested.
Cell-Free Fetal DNA
In a cell-free fetal DNA test, your blood is tested for chromosomal abnormalities in the baby. This is possible because cells from the placenta, an organ that provides nutrients to the baby in the womb, circulate in the mother’s blood. A positive test result can indicate genetic conditions such as Down syndrome.
Chorionic Villus Sampling
Between 10 and 14 weeks of pregnancy, your doctor may perform chorionic villus sampling, or CVS, which is a test for genetic abnormalities, such as Tay-Sachs disease, or chromosomal problems that can cause conditions such as Down syndrome.
In this test, the doctor inserts a thin, flexible tube called a catheter through the vagina into the cervix and placenta. Sometimes, a long, thin needle is inserted through the abdomen instead.
Ultrasound helps guide the doctor to the placenta, where he or she collects a sample of chorionic villi, tiny growths that carry genetic material. This sample is tested in a laboratory.
Rarely, a CVS test can increase the risk of miscarriage. Often, this test can be performed instead of amniocentesis, which is not performed until the second trimester.
First Trimester Screening
Between 11 and 14 weeks, a series of blood screening tests are performed to determine the baby’s risk for certain chromosomal abnormalities. One test determines levels of pregnancy-associated plasma protein A, the results of which can help your doctor assess the risk of miscarriage or low birth weight in your baby. Your doctor may also perform tests that determine the level of a pregnancy hormone called human chorionic gonadotropin. Low levels can indicate miscarriage or ectopic pregnancy, and high levels can indicate pregnancy with multiple babies.
The results of these tests, in combination with nuchal translucency screening performed with ultrasound, help identify the baby’s risk for Down syndrome and other chromosomal abnormalities.
An amniocentesis can test for genetic abnormalities, such as Down syndrome and cystic fibrosis. It can also determine if a baby has certain birth defects, including neural tube defects, which affect the baby’s brain and spinal cord.
In this test, a sample of amniotic fluid, which surrounds and protects the baby in the womb, is taken for analysis. A thin needle is inserted through the abdomen and into the uterus to the fluid-filled amniotic sac. A small amount of amniotic fluid, which contains cells, is extracted and analyzed in a laboratory for irregularities.
This procedure is performed after 16 weeks of pregnancy. Rare complications include amniotic fluid leakage, which can cause an infection in the mother’s uterus, and miscarriage.
Multiple Marker Screening
Also known as the quad screen or modified sequential screen, this blood screening procedure identifies four substances: alpha-fetoprotein, a protein produced by the fetus; human chorionic gonadotropin; the hormone inhibin A; and estriol, an estrogen produced by the baby. The results of this test can help determine if the baby has certain genetic conditions. It is performed between 15 and 22 weeks of pregnancy.