Alpha-fetoprotein (AFP) levels in maternal serum and amniotic fluid in singleton pregnant women in their 10th-25th week post last menstrual period.

Abstract

A rapid paper disk radioimmunoassay of the sandwich type was used to determine the levels of alpha fetoprotein (AFP) in 826 maternal serum samples derived from an equal number of singleton pregnant women prospectively investigated during their 10th-25th week past last menstrual period (LMP). In addition 396 amniotic fluid (AF) samples from the 14th-20th week post LMP were analyzed. Theoretical ranges of normal AFP variation are presented. The extreme range of AFP in serum samples from 236 nonpregnant blood donors varied fron .2-18.3 mcg/liter. Variability of AFP in maternal serum samples increased considerably with gestational progress. A specific low cut-off could not be defined until Week 15 post LMP because of the overlap between distribution of AFP levels in the pregnant and nonpregnant populations studied. However from Week 15 post LMP a feasibly low and decreasing frequency of maternal serum samples from normal pregnancies still had an AFP value below 10 mcg/liter; this value also represented the upper limit for 98.5% of the nonpregnant population. Thus 10 mcg/liter was found to be a useful cut-off from the 15th post LMP week below which pregnancy complications or severe gestation age miscalculations could be deduced. For AF AFP values a strong negative correlation between gestational age and AFP levels was found at least up to Week 20 post LMP.