Maternal and fetal serum transformed alpha-fetoprotein levels in normal pregnancy

Aim: To evaluate transformed alpha-fetoprotein (t-AFP) (a new molecular conformation of alpha-fetoprotein) levels in maternal serum and fetal serum in normal pregnancy. Methods: Prospective longitudinal study. Fifty pregnant women were studied in two groups: 25 were evaluated in each trimester of pregnancy and near term (12, 20, 32 and 36 weeks) and the other 25 were evaluated at the time of planned cesarean section at term. In the first group, maternal serum t-AFP was measured and in the second group, maternal and fetal serum t-AFP were analyzed. Results: Maternal serum t-AFP levels (medians) were 14.73 ng/mL in the first trimester, 28.29 ng/mL in the second trimester, 30.45 ng/mL in the early third trimester and 8.06 ng/mL in late pregnancy. t-AFP levels were significantly higher in maternal than in fetal serum (P < 0.001). There were no significant correlations between AFP and t-AFP levels in maternal versus fetal serum. Conclusions: t-AFP increases during pregnancy until the early third trimester and then falls before delivery. t-AFP levels are higher in maternal than in fetal serum which suggests that native AFP is transformed to t-AFP either in the mother or in the placenta.