Sources of 17α-hydroxyprogesterone (17-OHP) in human pregnancy were studied by measuring its plasma concentrations in blood samples of umbilical artery (UA), umbilical vein (UV), retroplacental space (RPS), maternal ovarian (OV) and maternal peripheral vein (PV) of eight patients in mid-pregnancy and five patients at term. The following means and standard deviations (sd) of 17-OHP were found for term pregnancy: UV, 22.2 ± 2.8; UA, 14.0 ± 2.3; PV, 6.6 ± 0.6; OV, 24.5 ± 5.0; and RPS, 29.7 ± 3.8 ng/ml. The mean (±sd) 17-OHP plasma levels at mid-pregnancy were: UV, 15.7 ± 4.3; UA, 11.9 ± 3.6; RPS, 17.0 ± 6.2; OV, 11.5 ± 2.0; and PV, 2.3 ± 0.3 ng/ml. The ovarian vein and RPS 17-OHP plasma levels which were 7- and 4-fold above PV levels in both mid-pregnancy and at term indicate placental and ovarian secretion of 17-OHP. Taking the different blood flows into account, it appears that at term the bulk of 17-OHP is produced by the placenta. Administration of hydrocortisone to six patients prior to cesarean section resulted in a decline of 17-OHP in PV, UA, and UV to 37, 19, and 16% of the control group respectively (p < 0.001). Five patients who sustained intrauterine fetal deaths had a fall of 44 to 70% in their PV levels, and two others bearing anencephalic fetuses had 17-OHP plasma levels of about 20% of the normal mean. Therefore, it is postulated that at term, fetal adrenal steroids provide a major portion of placental 17-OHP precursors.
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Tulchinsky et al. (1972) studied this question.