Alpha-fetoprotein values in amniotic fluid obtained during early amniocentesis (11-13 weeks).

OBJECTIVES:To determine the normal values of alpha-fetoprotein (AFP) in amniotic fluid between the gestational ages of 11 and 13 weeks and compare these with previously published values. METHODS:Amniotic fluid AFP was analyzed in 149 patients who had undergone amniocentesis between 11 +/- 0 and 13 +/- 6 weeks gestation as part of the pilot study of the Canadian Early and Mid-Trimester Amniocentesis Trial. Analysis was done using the Abbott IMX System (Abbott Laboratories Diagnostic Division, Abbott Park, Ill.). These values were then compared with previously published values. RESULTS:There is a progressive and linear rise in the amniotic fluid AFP concentration from 11 to 13 weeks gestation. The differences between each of the three gestational ages were statistically significant at the 0.05 level. The values differed significantly from those obtained by Crandall et al. [Am J Obstet Gynecol 1989;160:1204-1206], which were also consistently higher. CONCLUSION:Although reference points for 11, 12 and 13 weeks have been established, there are limitations to their clinical application.