Uterine activity in spontaneous labour and maternal peripheral plasma prostaglandin E2 and F2 alpha metabolites.

The relationship between maternal peripheral plasma concentrations of prostaglandin E2 and prostaglandin F2 alpha metabolites (bicyclo-PGEM and PGFM respectively) and the level of uterine activity in spontaneous labour was studied in 10 nulliparous and 10 multiparous women. Plasma prostaglandin metabolites were measured by radioimmunoassay. Uterine activity was quantified by computer analysis of changes in intrauterine pressure and expressed as mean active pressure (MAP). As labour progressed, both parity groups showed a significant rise in MAP which was associated with a significant increase in the levels of PGFM. However, the percentage rise in PGFM did not significantly correlate with the percentage rise in MAP. At all stages in labour PGFM and MAP levels were higher in the nulliparous group compared with the multiparous group. Bicyclo-PGEM levels showed no significant change in the nulliparous group but rose in late first stage/second stage in the multiparous group. Our observations support a role for prostaglandin F2 alpha in the generation of uterine activity in spontaneous labour. However, further study is required to elucidate the mechanisms controlling prostaglandin production by the fetal membranes and decidua in vivo, and how this relates to maternal peripheral plasma prostaglandin metabolite concentrations and the level of uterine activity.