Low maternal serum a-fetoprotein (MSAFP) is associated with

(B).Second-trimesterscreening(15-18 wk) of maternal serum a-fetoprotein (MSAFP) values is used to screen for open neural tube defects. About 90% of affected pregnanciescan be detected by an elevated MSAFP value. Gastroschisis,omphalocele. congenitalnephrosis, twins, and other abnormal conditions can also be identified. Low MSAFPis associated with incorrect gestational age estimates, trisomy 18 or 21, and intrauterine growth restriction