Obstetrics / Pregnancy — Prenatal Screening for Birth Defects

There is a wide array of screening tests in pregnancy. Screening tests are performed to assess a person's risk for a condition affecting pregnancy and the fetus. These tests do not provide a diagnosis, instead identifying couples who should be offered diagnostic testing.

Examples of conditions for which screening is possible are Down syndrome, Trisomy 18, and cystic fibrosis.

WHC offers nuchal translucency (NT) testing as well as blood testing to identify carriers of such conditions. These tests are optional.

Nuchal translucency

This is a screening test used to identify pregnancies at higher risk for Down syndrome and Trisomy 18. It involves a combination of ultrasound and blood testing to determine these risks. The test is performed between 11 weeks to 13 weeks 6 days (after a prior ultrasound has been performed to verify dating of the pregnancy). The results are available in 7 to 10 days.

Quad test

This test provides a similar risk assessment for Down syndrome, Trisomy 18, and neural tube defects (spina bifida and anencephaly). It is performed between 15 and 20 weeks, and results are available in 7 days. Given the higher chance for detection with the nuchal translucency test, the quad test is less frequently used.

Carrier testing

Recessive conditions require two mutations (one from each parent) for the disease to be present. Individuals with one copy of the mutation are called carriers. Each individual is born with, on average, 8 to 10 recessive mutations. Ethnicity can provide a clue for certain conditions. Two conditions are considered prevalent enough to offer universal screening for patients: cystic fibrosis and spinal muscular atrophy. Couples electing to pursue testing can have their blood tested to identify their status. If the woman is a carrier, we recommend testing her partner. Amniocentesis would be offered to couples identified as carriers.

Those couples identified with an elevated risk (for Down syndrome or Trisomy 18) are referred for genetic counseling and diagnostic testing (such as amniocentesis or chorionic villus sampling) with perinatologists (high-risk obstetricians).