Natural prostaglandins for induction of labor and preinduction cervical ripening.

Prostaglandin (PG) E2 has superseded all other natural prostaglandins for induction of labor and pre-induction cervical ripening. This evolution and its rationale are briefly described. PGE2 has been administered intravenously, orally, vaginally, endocervically, and extra-amniotically for induction of labor. All of these, except the intravenous route, have also been explored for pre-induction cervical ripening. The distinction between formal induction and pre-induction is not always clearly made with many studies pursuing both goals at once. Nevertheless, the effectiveness of PGE2 to achieve ripening and induction is currently beyond doubt. In women with unfavorable induction prospects PGE2 results in lower rates of failed induction and higher rates of delivery within a reasonable interval than amniotomy and/or oxytocin. This also applies to women with prelabor rupture of the membranes, but the relative advantages of PGE2 over traditional methods are less clear for women with a favorable cervix. Vaginal administration of PGE2 has superseded virtually all other routes of PGE2 administration except the endocervical route, which tends to give variable results depending on spillage from the endocervical canal. Doses and formulations of vaginal PGE2 with various gels, tablets, pessaries and slow release inserts have varied widely and continue to do so. There is currently no evidence for the superiority of one PGE2 preparation over another.