The relation between the release of prostaglandins at amniotomy and the subsequent onset of labour.

Maternal peripheral plasma levels of 13,14-dihydro-15-keto-prostaglandin F (PGFM) were measured in 16 women following amniotomy performed for the induction of labour at term. After 5 1/2 hours, seven patients were in established labour (Group I) but the remaining nine patients required an intravenous infusion of oxytocin (Group II). An initial rapid rise in PGFM concentrations within five minutes of amniotomy occurred in all women and, therefore, the onset of labour does not appear to be a direct consequence of this initial increase. In Group I there was a significant increase in PGFM concentrations between five and 30 minutes after amniotomy and from 30 minutes to the time at which the last sample was collected; these later rises were associated with the onset and progress of labour in these women. These increases in PGFM concentrations did not occur in patients in Group II. The reason for this difference in response to amniotomy is as yet unclear.