Fetal and Maternal Serum Levels of Steroid Sulfates, Unconjugated Steroids, and Prolactin at Term Pregnan and in Early Spontaneous Labor*

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Abstract
In 33 pregnancies, blood samples were collected from the maternal vein and umbilical cord artery and vein during cesarean section performed at 37–41 weeks of gestation. Serum concentrations of unconjugated steroids and PRL were measuredby RIA, and concentrations of steroid sulfates were measured by gas chromatography. Nineteen women (group A) were operated on in the absence of signs of the beginning of labor. Paired comparisons revealed large cord arteriovenous differences in the serum levels of steroid sulfates (nanograms per ml, mean ± SEM): pregnenolone sulfate, 98 ± 25; dehydroepiandrosterone sulfate, 160 ± 51; 16a-hydroxydehydroepiandrosterone sulfate, 621 ± 150; and estriol sulfate, 169 ± 20, demonstrating marked utilization of steroid sulfates by the placenta from the fetal circulation at term. Smaller but significant cord arteriovenous differences were also found in the serum levels of unconjugated pregnenolone (3.0 ± 1.1), dehydroepiandrosterone (2.15 ± 0.53), and cortisol (10.0 ± 2.4). On the contrary, levels of progesterone and estradiol were significantly higher in cord venous than in cord arterial blood, indicating their placental secretion into the fetal circulation. In the remaining 14 pregnancies, cesarean section was performed in early spontaneous labor (group B). The only significant difference in maternal and fetal steroid concentrations between groups A and B was a lower mean level of dehydroepiandrosterone sulfate (905 ± 160) in the cord arterial serum samples in group B compared to those in group A (1310 ± 130; P < 0.05). Thus, these results did not give any evidence for increased fetal adrenal activity at the onset of labor. Fetal or maternal serum PRL levels were not found to differ in subjects before or at the onset of labor. No significant correlations between the fetal serum levels of PRL and steroids could be found.