Diagnostic Tests
When an abnormality on a screening test is found, it usually requires a diagnostic test to know more. These tests have additional risks and are not considered routine for all pregnant women.
Chorionic villus sampling (CVS)
Chorionic villi are tiny outgrowths from the placenta. They attach to the mother's uterus and allow the placenta to form. During CVS, a sample of this tissue is removed for study.
This test is used to diagnose abnormalities in the fetus and is done during the ninth to eleventh week of pregnancy.
Amniocentesis
Amniocentesis involves withdrawing and testing a small amount of the amniotic fluid surrounding the fetus. This fluid provides information such as:
- Blood incompatibilities between mother and baby (Rh disease)
- Genetic defects such as Down syndrome and cystic fibrosis
- Defects leading to abnormal brain and spinal cord development
- Fetal maturity near the end of pregnancy
The procedure is usually done with sonography to guide the needle and prevent injury to the fetus, cord and placenta.
Amniocentesis is considered 99.5 percent safe and usually involves little risk. It is not a routine test, however, and is only used to detect a highly likely medical problem.
Fetal Maturity Tests
Amniotic fluid tests late in pregnancy can determine lung maturity, which has more to do with a baby's ability to survive than its birth weight. This test is usually done sometime after 35 weeks. It is especially helpful when complications call for an early birth or when the due date is uncertain.
Babies born with immature lungs can suffer from respiratory distress syndrome, a leading cause of death in newborns.
