The ED90 of Prophylactic Oxytocin Administration in Low vs. High-Risk Parturients in Terms of Post-Parturition Uterine Tonicity; An Up-Down Sequential Allocation Dose-Response Study

This study was performed to determine and compare the ED90 of prophylactic oxytocin (OX) infusion after delivery of the placenta during cesarean section (CS) in low- and high-risk parturients for uterine atony.

This experimental study was a single-blind and dose-response study using a 9:1 biased-coin sequential allocation method to estimate the ED90 of prophylactic infusion of OX in women with high and low risk for uterine atony who underwent CS. The total administrated OX dose of each patient was determined in the two study groups. The primary outcome was the ED90 for desirable uterine tone based on the opinion of the in-charge obstetrician. The number of subjects receiving supplemental uterotonics was compared.

In the low-risk group, three (3.7%), out of the 41 parturients, did not achieve a satisfactory suitable response to OX dose of 9; on the other hand, 24 high-risk parturients (58%) did not achieve a satisfactory and reasonable response to OX dose of 9. The OX ED90 was significantly greater for the high risk-group (11.55 units, 10.39-14.86) than the low-risk group (8.13 units, 8.31-9.56). Fisher’s exact probability test showed a significant difference in ED90 of OX between the two groups (P=0.02).

The present study results showed that the mean ED90 of OX in low-risk parturients was significantly lower than that of high-risk ones. We suggest differentiation between low-risk and high-risk parturients in the guidelines of OX administration.