Relation of gestational age, maternal body weight and age or serum α-fetoprotein and human chorionic gonadotropin at second-trimester

Serum levels of α-fetoprotein (AFP) and human chorionic gonadotropin (hCG) were measured in serum samples of 1,964 pregnant Japanese women whose gestational age and singleton pregnancy were confirmed by ultrasound examination during the first trimester of pregnancy. Statistical analysis of log-linear regression to calculate multiples of the median (MoM) was accomplished by the SAS statistical method. The levels of the two analytes noticeably decreased as maternal body weight increased. However, maternal age did not have a significant effect on either of them. The MoM formulae were as follows: MSAFPMoM = AFP/exp (0.861 + 0.0685 x gestational age (weeks) - 0.00572 x body weight (kg)). MShCGMoM = hCG/exp (6.12-0.787 x gestational age (weeks) - 0.00613 x body weight (kg)). Gestational age and maternal body weight should be considered as regression functions for the adjustment of serum levels in risk estimation of fetal anomalies and fetal demise in Japan.