The effect of estrogen priming on induction of labor with prostaglandins.

A double-blind, randomized study was designed to determine whether estrogen "priming" of the unripe cervix followed by prostaglandin induction of labor would have a synergistic effect on cervical ripening and improve the success rate of induction. One hundred near-term patients with Bishop scores less than or equal to 4 received an intramuscular injection of either 10 mg of estradiol valerate or a placebo 48 hours prior to induction of labor with oral prostaglandin E2. The serial changes in Bishop scores were very similar in both groups. The success rate of induction in the study group (69.8%) was not statistically different from that in the control group (61.9%). The duration of labor was 9.9 +/- 4.1 hours in the study group versus 9.1 +/- 3.7 hours in the control group (not significant). This study showed that 10 mg of estradiol valerate had no detectable effect on the unripe cervix near term and did not show a synergistic effect with prostaglandins during induction of labor.