INTERRELATIONSHIPS OF CIRCULATING MATERNAL STEROID CONCENTRATIONS IN 3RD TRIMESTER PREGNANCIES .1. C-21 STEROIDS - PROGESTERONE, 16ALPHA-HYDROXYPROGESTERONE, 17ALPHA-HYDROXYPROGESTERONE, 20ALPHA-DIHYDROPROGESTERONE, DELTA-5-PREGNENOLONE, DELTA-5-PREGNENOLONE SULFATE, AND 17-HYDROXY-DELTA-5-PREGNENOLONEL

This report describes aggregate time trend effects of advancing gestational age on circulating maternal concentrations of progesterone (P), 16α-hydroxyprogesterone, 17α-hydroxyprogesterone (17P), 20α-dihydroprogesterone (20P), Δ5-pregnenolone sulfate, Δ5-pregnenolone (Δ5P), and 17-hydroxyA5-pregnenolone (17Δ5P) in a sequential series of 153 blood samples obtained from 19 normal pregnant women ranging from 26-40 weeks gestational age. After logarithmic transformations and curve-fitting procedures, significant differences in slopes were sought and tested by multivariate least squares methods. All steroids, except for 17Δ5P, were markedly elevated above previously reported nonpregnancy concentrations and plotted as positive sloping curves. Log (P) and log (20P) concentration-time curves describe single segment linear curves of similar slope (P > 0.05) and are consistent with the hypothesis that 20P is a metabolite of P, sharing in a relatively stable interconversion with P as the major placental secretory product. Log (17P) describes a single segment linear curve that is significantly steeper than both log (P) (P < 0.05) and log (20P) (P < 0.05) and probably reflects upon the markedly different combined fetal placental mechanisms known to regulate 17P production. Log (16α-hydroxyprogesterone) is best described by a threelinear segment-fitted curve with join point estimates at 32.7 ± 0.93 and 37.0 ± 0.96 (SE) weeks, a sharply positive sloping midsegment, and relatively shallow end segments; this pattern closely resembles the time course of several known third trimester intrauterine maturational processes. Log (Δ5pregnenolone sulfate) and log (Δ5P) have similar positive sloping curves consistent with an equilibrium thought to exist between these two steroids, with Δ5P believed to be the major placental secretory product. Log (17Δ5P) showed no discernable aggregate time trend effect, demonstrated widely undulating concentrations in nonpregnant ranges, and is probably of maternal adrenal origin. © 1979 by The Endocrine Society.