Maternal serum alpha-fetoprotein in normal pregnancy at 11-13 weeks' gestation

To establish a reference distribution of maternal serum alpha-fetoprotein (AFP) at 11-13 weeks' gestation and define the contribution of maternal variables that influence the measured concentration of AFP.

Serum concentration of AFP at 11-13 weeks was measured in 1,500 singleton pregnancies which were not complicated by hypertensive disorders or diabetes mellitus and resulted in the live birth at or after 37 weeks of phenotypically normal neonates with birth weights above the 5th and below the 95th percentile. Multiple regression analysis was used to account for maternal characteristics that influence the measured concentration of AFP and a distribution of log multiples of the median (MoM) values was fitted.

Log(10) AFP increased with gestational age, decreased with maternal weight and was significantly affected by maternal racial origin, smoking status and method of conception. Compared with values in Caucasian women who were non-smokers and conceived spontaneously, AFP MoM was on average 23% higher in Afro-Caribbeans and 8% lower in East Asians, 11% higher in smokers and 10% higher in those conceiving by in vitro fertilization.

In normal pregnancies at 11-13 weeks, serum AFP increases with gestational age and is affected by maternal race, weight, smoking status and method of conception.