Raised prostaglandin levels in the third stage of labor.

Serial measurements of maternal peripheral plasma concentrations of 13,14-dihydro-15-keto-prostaglandin F (PGFM) and oxytocin were made during the three stages of labor and in the immediate puerperium. PGFM levels increased a labor progressed, and reached maximal levels before placental separation had occurred. The mean value in the second stage of labor was significantly higher than that in the first stage (p less than 0.01); similarly, the value 5 minutes after delivery, before expulsion of the placenta, was significantly greater than that in the second stage of labor (p less than 0.01). There was no significant difference between the mean PGFM concentration at placental separation and the level 5 minutes after delivery or in the second stage of labor. Two hours after delivery of the placenta, PGFM levels were not significantly different from values observed in the first stage of labor. Peripheral plasma concentrations of oxytocin did not change significantly at any stage of labor or 2 hours post partum. These results suggest that prostaglandins have a role in the third stage of labor, and this finding may have important clinical implications.

Is oxytocin involved in parturition?

Peripheral plasma levels of oxytocin were determined in women during pregnancy and labour. There was a significant increase in maternal plasma oxytocin with advancing gestation but no significant change in levels at any stage of labour. Oxytocin concentrations in umbilical cord plasma were measured after spontaneous vaginal delivery and at elective caesarean section. A significant arteriovenous difference, with higher arterial levels, was found in both groups and the values after labour were significantly higher tha at elective caesarean section. These findings suggest that the fetus is able to produce oxytocin which may play a role in human parturition.

Release of prostaglandins after amniotomy is not mediated by oxytocin.

The rise in peripheral plasma levels of 13,14-dihydro-15-keto-prostaglandin F (PGFM) following amniotomy has now been shown to be maximal within five minutes of the procedure, and levels remain elevated for at least 30 minutes. There was no change in plasma oxytocin levels with amniotomy and therefore a local mechanism for prostaglandin release has been postulated.