Concentrations of Progesterone in the Plasma of Mothers and Infants at Time of Birth

Abstract

A highly sensitive method utilizing competitive protein binding was used to study concentrations of progesterone in the plasma of mothers, in umbilical cord plasma, and in the plasma of full-term and premature infants in the immediate postpartum period.Blood samples were obtained from 20 mothers during labor and from the cords of their infants at delivery. Most of these infants were also studied at 2 or 3 days of age. For purposes of comparison, a second series of samples was obtained from control subjects using needle aspiration to obtain samples from the umbilicus; 14 samples were studied.In the mothers, concentrations of progesterone in plasma ranged from 46 to 387 ng/ml (mean: 129±78 SD) ; in cord blood, progesterone levels ranged from 440 to 2,000 ng/ml (mean: l,030±412 SD); and in blood from the umbilical vein, concentrations of progesterone ranged from 310 to 720 ng/ml (mean: 562±140 SD).A total of 27 full-term newborns was studied at 24, 48, and 72 h of life. In four cases, blood was obtained from the same infant at 12, 24, and 72 h of life. The highest concentrations of progesterone were noted during the first 24 h of life, with levels ranging from 13 to 32 ng/ml (mean: 19 ng/ml) at 12 h, and from 2 to 32 ng/ml (mean: 16 ng/ml) at 24 h. By day 2, levels of progesterone had decreased to 3-20 ng/ml (mean: 10 ng/ml) and by day 3 were reduced to 0-16 ng/ml (mean: 8 ng/ml).Thirty-two premature infants, with birth weights of from 1,317 to 2,465 g, and ranging in gestational age from 30 to 40 weeks, were also studied. In several cases serial blood samples were obtained by the same methods used with the full-term infants. Two sets of twins were included. In premature infants, as with full-term newborns, a range of 4-34 ng/ml (mean: 14 ng/ml) was found at 12 h of life, decreasing rapidly to 2-6 ng/ml (mean: 3 ng/ml) by 24 h of life. These low concentrations persisted throughout days 2 and 3.There was no significant difference between concentrations of progesterone in plasma in full-term and premature infants at 2-3 days of age. It appeared that premature infants were as able to clear progesterone from the plasma as were the full-term infants. SpeculationThe data obtained in this study support the concept that large amounts of progesterone are delivered from the placenta to the fetus. This compound may be a precursor of C-21 steroids such as cortisol, synthesized by the fetal adrenal. Progesterone has also been shown to effect respiration in animals GONLY, MORRISON, SANDBERG and CLEVELAND 77and man [7,8,14,15] and an effect on neonatal respiratory mechanisms and disease may occur, although this has not been demonstrated.Maternal blood has a relatively large concentration of progesterone which diminishes rapidly following delivery of the placenta. Presumably the compound exerts some effect in the maintenance of pregnancy. Its exact role has not been established.

Plasma Mineralocorticoids, Glucocorticoids, and Progestins in Premature Infants: Longitudinal Study during the First Week of Life

“…The rapid postnatal decline of progesterone levels in premature infants is in agreement with reports in term infants and reflects the predominant placental origin of this steroid (2,3). Our data are comparable to those of Conly et al (36) who studied only three premature infants serially, and to random data of Forest and Cathiard (37) and Tapanainen et al (38).…”

Cortisol Binding to Proteins in Plasma in the Human Neonate and Infant

“…The maternal over fetal total plasma cortisol ratio has been evaluated as 3:1, whereas the ratio for the unbound hormone was found to be 1: 1 (1). This unbound form may represent the fraction of the hormone exchangeable through the progesterone (11). Neonatal cortisol level in plasma is relatively low (23,24) and in agreement with the available specific binding capacity given by our data.…”

Plasma Aldosterone Concentration at Delivery and during the Newborn Period

“…The kidneys are able to concentrate urine to about half the full capacity (66). High circulating levels of progesterone may also aggravate sodium loss (68,69).…”