this population-based study analyzes maternal serum alpha-fetoprotein ( msafp ) distributions for 20 cases of gastroschisis and 13 cases of omphalocele occurring in singleton pregnancies from among 72,782 second-trimester pregnancies in maine and rhode island screened consecutively between january 1 , 1979 and february 28 , 1987 .
C0032961
pregnancies
C0032980
second-trimester