The composition of amniotic fluid in pregnancies complicated by fetal anencephaly or spina bifida.

The concentration of amniotic fluid glucose, total protein, sodium, potassium, calcium, magnesium and phosphate as well as amniotic fluid osmolality were measured in normal second trimester pregnancies and in second trimester pregnancies complecated by fetal anencephaly or spina bifida. Amniotic fluid glucose concentration was low in anencephaly, while phosphate and total protein were high; calcium concentration and osmolality were slightly elevated with spina bifida. The application of these findings to antenatal diagnosis are discussed.