MATERNAL PLASMA PROGESTERONE LEVELS FALL AFTER RECTAL ADMINISTRATION OF ESTRIOL

Maternal plasma unconjugated estriol (E(3)), progesterone (P), and est radiol (E(2)) levels were measured at 30-min intervals for 6 h after t he rectal administration of a 100-mg E(3) or placebo suppository to 28 pregnant women at term. Mean plasma unconjugated E(3) levels showed a sustained rise approximately 50% above baseline levels 2 h after rect al E(3) administration (P < 0.003). There was a simultaneous sustained fall of approximately 20% in mean plasma P levels (P < 0.05); the fal l in mean P levels was greatest in the women who delivered within 48 h of E(3) suppository administration (P < 0.05). There was no change in mean plasma E(2) levels. This study demonstrates that a significant r apid increase in maternal circulating E(3) levels can be obtained by t he rectal administration of E(3), and that this increase in maternal E (3) levels is associated with a decrease in circulating P levels.