Interrelationships of Circulating Maternal Steroid Concentrations in Third Trimester Pregnancies. I. C21Steroids: Progesterone, 16α-Hydroxyprogesterone, 17α-Hydroxyprogesterone, 20α-Dihydroprogesterone, Δ5-Pregnenolone, Δ5-Pregnenolone Sulfate, and 17-HydroxyΔ5-Pregnenolone

Abstract

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-hydroxyΔ⁵-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.