Second-trimester maternal serum alpha-fetoprotein levels in pregnancies associated with gastroschisis and omphalocele.

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. Median values (and ranges) for the two lesions were 4.1 multiples of the median (0.5-29.8) for omphalocele and 7.0 multiples of the median (3.6-13.5) for gastroschisis. The MSAFP distributions for the two conditions were both log-Gaussian, and the log standard deviation was smaller for gastroschisis than for omphalocele. The MSAFP screening sensitivity was greater for gastroschisis than for omphalocele at any given cutoff, and the overall sensitivity of this screening process for detecting open ventral wall defects will differ, therefore, depending upon the relative proportion of gastroschisis and omphalocele cases that occur in the screened population.