Alpha-fetoprotein concentration in amniotic fluid during the last trimester in normal pregnancies and in pregnancies with severe fetal abnormalities.

The concentration of alpha-fetoprotein (AFP) in the amniotic fluid was studied during the last trimester of pregnancy. 129 samples of amniotic fluid were collected by transabdominal amniocentesis in 94 pregnant women. Only women with uncomplicated pregnancies giving birth to normal infants at term were included. The 90% reference interval was calculated and a distinct decrease in the amniotic fluid AFP concentration was found during the last trimester. An AFP concentration above the 90% reference interval was found in 8 out of 10 cases of anencephaly. Normal AFP concentration was found in a case of congenital heart disease with severe oedema, and a low concentration was found in a case of Down's syndrome (Trisomy 21).