Serum concentrations of progesterone and 5 alpha-pregnane-3,20-dione during labor and early post partum.

Serum 5 alpha-pregnane-3,20-dione (5 alpha DHP) and progesterone (P) concentrations were studied in 11 women with uncomplicated pregnancies and deliveries during spontaneous labor and immediately after delivery. Blood samples were drawn 3-6 times during labor, as soon as possible post partum and 1, 3, 6 and 12 h post partum. P and 5 alpha DHP were analysed using RIA methods. There were no significant changes during labor in serum concentration of P and 5 alpha DHP, the values being 366 nmol/l +/- 25 SE and 128 nmol/l +/- 16 SE respectively. Whereas an earlier study has shown a significant decrease in 5 alpha DHP serum concentration between late pregnancy and spontaneous labor, this study showed no decrease during labor, indicating that the decrease occurred before the onset of labor. After parturition, the elimination of P from serum was faster and proportionally greater than for 5 alpha DHP, with a half-life of 38 min for P and 58 min for 5 alpha DHP. About 2-3 h post partum the serum concentrations stabilized just above luteal phase values. 12 h post partum, P and 5 alpha DHP were 12% and 23% respectively of pre-partum values.