2,3-diphosphoglycerate in normal and pathologic pregnancy: relationship to neonatal weight.

2,3-Diphosphoglycerate levels were assayed in 154 pregnant women in third trimester (61 normal, 52 diabetic, 19 with gestational hypertension, 7 with fetal macrosomia, and 15 with idiopathic fetal underdevelopment). A correlation was found between 2,3-diphosphoglycerate levels and birth weight (absolute and relative birth weight or birth weight expressed as percentile), which was negative in normal patients evaluated in the last 7 days before delivery (r = 0.38; p = 0.04) and positive in diabetic patients (evaluated in the third trimester and in the last 7 days before delivery) and in patients with gestational hypertension (evaluated in the third trimester) (r and p values differ according to whether birth weight is expressed as absolute, relative, or a percentile). No correlation was found between 2,3-diphosphoglycerate levels and birth weight in patients with neonatal underdevelopment or macrosomia of unknown origin. On the basis of these results we hypothesize that in some conditions the fetus can influence maternal 2,3-diphosphoglycerate levels and hence its own oxygen supply and growth in utero.