Labor-augmenting drug may contribute to reduced effect in controlling postpartum bleeding

The drug oxytocin is used for two purposes during childbirth. First, oxytocin is used to augment labor when the obstetrician feels the labor is not advancing appropriately or, in some cases to induce labor. In this way, oxytocin works to help the labor progress. Second, oxytocin is frequently used at the end of delivery to control bleeding by causing the uterus to contract.

Maternal mortality rates have increased in the United States since 2000, according to the Association of Reproductive Health Professionals (ARHP). The rate has nearly doubled since 2000, hovering between 12 and 15 deaths per 100,000 women. Severe and life-threatening complications have also increased 27 percent between 1998 and 2005. The leading cause of maternal deaths in the United States and throughout the world is postpartum hemorrhage.

"With this in-vitro study, we were able to confirm clinical research data demonstrating an association between the use of oxytocin for an extended time to augment labor and the need for a greater dosage of oxytocin or perhaps alternate medications to stop a mother's hemorrhage after delivery," said study author Mrinalini Balki, M.D., staff anesthesiologist at Mount Sinai Hospital, Toronto and associate professor at the University of Toronto. "Oxytocin is a 'double-edged sword' because while it helps to move labor along, after prolonged use, the mother becomes desensitized to it."

Dr. Balki further detailed, based on the previous research done by her group, that the dosage of oxytocin required to help the uterus contract after elective cesarean delivery in women who received no prior oxytocin was minimal. However, women who received oxytocin for a prolonged time to augment labor required nine times more oxytocin to produce effective uterine contraction. These mothers also bled twice as much as the elective cesarean section group.

In this study, samples of uterine muscle from 62 women who had elective cesarean deliveries were treated with different doses of oxytocin for two, four, six and 12 hours while noting the strength and frequency of contractions induced by additional oxytocin administration. The study found that increasing the dose and duration of oxytocin treatment from two to 12 hours significantly decreased the strength of the contractions, indicating that excessive and prolonged exposure of the uterus to oxytocin resulted in a desensitization effect, reducing the effectiveness of the drug.

"This research provides insight into re-consideration of the choice and dose of uterotonic medications post-delivery," continued Dr. Balki. "It is suggested that anesthesiologists may need to use higher doses of oxytocin after cesarean deliveries in women with oxytocin augmented labors, or may need to resort to second-line agents for controlling uterine bleeding. However, further clinical studies are warranted to confirm these findings."