Prenatal testing for maternal serum alpha-fetoprotein.

The maternal serum alpha-fetoprotein level should be measured in all pregnant women at 16 to 20 weeks of gestation. Elevated alpha-fetoprotein levels require evaluation by ultrasonography and, sometimes, amniocentesis to detect neural tube defects. Low alpha-fetoprotein levels may be associated with chromosomal anomalies and should be evaluated with amniocentesis. Alpha-fetoprotein testing is cost-effective, and medicolegal liability makes it imperative to offer this screening test to all pregnant women.