Postpartum intrauterine pressure studies of the uterotonic effect of oral misoprostol and intramuscular syntometrine

Abstract

Objectives: To investigate the effect of oral misoprostol in dosages varying from 200 microg to 800 microg on postpartum uterine contractility and to establish their side effects.

Design: A prospective descriptive study.

Participants: Fifty-seven women who delivered vaginally after spontaneous labours not requiring augmentation.

Methods: Within 5 minutes of delivery of the placenta, a calibrated Gaeltec catheter with an intrauterine pressure transducer at its tip was inserted transcervically into the uterine cavity. Cumulative uterine activity was recorded for 30 minutes in each woman before administering the oral misoprostol tablets and continued for a further 90 minutes after its administration. Thus each woman acted as her own control regarding changes in uterine contractility. Uterine activity was recorded on a Sonicaid Meridian fetal monitor, which measures active contraction area automatically. The incidence of side effects was also recorded.

Results: There was no statistical difference (P = 0.887) in the adjusted mean difference in cumulative uterine activity following all the doses of oral misoprostol, compared with intramuscular syntometrine, the largest difference being seen in oral misoprostol 200 microg (adjusted mean difference -2282 kPas s, 95% CI -7954 to 3390 kPas s). The mean onset of action of oral misoprostol (6.1, SD 2.1 min) was significantly slower than that of intramuscular syntometrine (3.2, SD 1.5 min; P = 0.002), but their durations of action were similar (P = 0.637). In the misoprostol group the commonest side effects were shivering (36%) and a rise in body temperature above 38 degrees C (40%). In the syntometrine group, the most commonly observed side effect was moderate uterine pain (nine out of ten women) and a rise in diastolic blood pressure of 20 mmHg (two out of ten women).

Conclusion: The results of this study show that oral misoprostol has a definite uterotonic effect on the postpartum uterus. At doses of 200 microg to 400 microg, oral misoprostol has a similar uterotonic effect to intramuscular syntometrine. Higher doses of oral misoprostol are associated with significantly more side effects.