The relationship between maternal serum and amniotic fluid alpha-fetoprotein in women undergoing early amniocentesis.

alpha-Fetoprotein levels were measured on 148 paired samples from the maternal serum and amniotic fluid in women greater than or equal to age 35, who were undergoing early amniocentesis (12 to 14 weeks) for chromosomal analysis. These 148 women were white, weighed less than 200 pounds, had no serious medical problems, and did not have a fetal abnormality detected by ultrasonography or karyotype analysis. There was a significant rise in the maternal serum alpha-fetoprotein concentration from 12 to 14 weeks' gestation. Amniotic fluid alpha-fetoprotein peaked at 13 weeks and then significantly declined by 14 weeks' gestation. Similar to reports from normal pregnancies at 16 and 17 weeks, we found no correlation between the maternal serum and amniotic fluid alpha-fetoprotein levels between 12 and 14 weeks. Amniotic fluid alpha-fetoprotein levels cannot be predicted by levels in the maternal serum in pregnancies between 12 and 14 weeks' gestation.