[Changes in steroids in amniotic fluid in relation to the initiation of labor]

To study the changes in steroid concentrations in amniotic fluid (AF) in relation to the initiation of parturition, eleven steroids in AF which included cortisol(F), progesterone (P4), 20 alpha-dihydroprogesterone, free(f-) and conjugated(c-) pregnenolone, DHA, estradiol(E2) and estriol(E3) were measured by RIA. Experiment 1: Samples were obtained at I) elective cesarean section (not in labor, n = 9), II) vaginal delivery after the spontaneous onset of labor (in labor, n = 13). Experiment 2: AF were collected serially from each individual at A) the artificial rupture of the membrane before the onset of labor, B) the initiation of labor and C) second stage of delivery. Samples of B and C were obtained with a catheter which was placed in the uterine cavity at the rupture of the membrane. The mean concentrations of F,c-E2,f- and c-E3,DHA in I were significantly higher than those in II. In experiment 2, except for P4, all steroid concentrations tended to increase during the course of labor. The levels of F increased significantly from A to C but not from A to B. Free DHA increased from B to C. The percentage increase in steroid levels was also caliculated and it was found that the steroid increase from A to B was f-E2 while P4 decreased. E2/P4 ratio increased significantly from A to B. These results suggested that the increase in F and DHA may be due to the fetal response to the stress of labor. A possible role of increased E2 and decreased P4, and subsequently increased E2/P4 ratio, in AF on the onset of labor is suggested.