SAN DIEGO – Women with a body mass index of 35 kg/m2 or greater responded poorly to oxytocin treatment for arrest of dilatation, compared with leaner subjects, results from a single study showed.
"Maternal obesity is increasingly prevalent and is associated with high rates of dysfunctional labor and cesarean delivery, outcomes that are not completely attributable to high fetal weight," researchers led by Dr. Shelly Soni wrote in a poster presented during the annual meeting of the American College of Obstetricians and Gynecologists. "Obesity may inhibit uterine contractility and labor progress."
To test their hypothesis that oxytocin administered to treat arrest of dilatation is less effective in obese women, compared with lean women, Dr. Soni and her associates reviewed an electronic database for women with singleton term pregnancies in cephalic presentation who labored and delivered at Flushing (N.Y.) Hospital Medical Center between July 2004 and August 2011. After excluding patients with medical complications or prior cesarean delivery, the researchers identified 118 consecutive cases diagnosed with arrest of dilatation and grouped them into one of four body mass index (BMI) classifications: BMI of less than 25 kg/m2 (group A; n = 30); BMI of 25-29.9 kg/m2 (group B; n = 33); BMI of 30-34.9 kg/m2 (group C; n = 32), and BMI of 35 kg/m2 or greater (group D; n =23).
An investigator blinded to the patients and to the groups constructed labor curves for each patient. Successful treatment of an arrest of dilatation was defined as attainment of full dilatation.
Dr. Soni, a third-year resident in the department of obstetrics and gynecology at the center, reported that none of the four groups differed significantly in birth weight, gestational age, parity, or maternal age. However, successful treatment of the arrest disorder was achieved in 90% of women in groups A and B, 72% of women in group C, and just 39% of women in group D.
"The amount of oxytocin used as well as time to delivery or cesarean decision after starting oxytocin was significantly higher in group D (P = .001) [and] the cesarean delivery rate was directly related to maternal BMI across the cohort (P = .001)," the researchers noted. "Among patients who had further dilatation after beginning oxytocin, the frequency with which the post-arrest slope was equal to or greater than the pre-arrest slope was inversely related to maternal BMI."
They went on to speculate that obesity "may inhibit uterine contractility and the uterine response to oxytocin, which in turn may explain our results, and the high rates of dysfunctional labor and cesarean delivery among obese women."
In an interview, Dr. Soni noted that one limitation of the analysis was that "it was not designed to see if a higher dose of oxytocin would be effective in obese women."
Dr. Soni said she had no relevant financial conflicts to disclose.