Rapid increases in plasma prostaglandin concentrations after vaginal examination and amniotomy.

Peripheral plasma concentrations of 13,14-dihydro-15-keto prostaglandin F (PGFM) were measured in three groups of women after the 37th week of pregnancy. Samples were taken before and five minutes after (a) amniotomy, (b) vaginal examination with sweeping of the fetal membranes, or (c) vaginal examination without sweeping of the membranes. Each procedure significantly raised the circulating PGFM levels, although amniotomy and vaginal examination with membrane sweep were more potent stimuli than vaginal examination alone. These findings suggest that there is a considerable potential for rapid increases in prostaglandin production during late pregnancy and provide a possible explanation for the fact that amniotomy and vaginal examination with membrane sweep often initiate labour.