A prospective observational study comparing intrauterine pressure during the second stage of labor: Does body mass index affect pressure generated during pushing?

To compare intrauterine pressure generated during pushing as measured by an intrauterine pressure catheter in the first and second stages of labor in obese patients (body mass index [BMI] ≥ 35 kg/m2) and nonobese (BMI < 35 kg/m2).This was a prospective observational study of patients in labor at term. Peak intrauterine pressure was measured during a Valsalva maneuver in the first and second stages of labor, both during a contraction and at rest and compared between obese and nonobese patients. Pushing pressure, defined as the mean of the highest three out of five peak pressures attained minus the intrauterine resting pressure were also compared for the two groups.A total of 115 patients were enrolled: 50 (43.5%) obese and 65 (56.5%) nonobese. We found pushing pressures were significantly less in obese patients both with risk difference (RD) = 13.71 (95% confidence interval [CI]: 5.53, 21.90) and without RD = 12.19 (95% CI: 4.46, 19.91) a uterine contraction compared to the nonobese patients in the second stage of labor. This effect persisted after controlling for confounding variables.Obese patients with BMI ≥ 35 kg/m2 generated lower intrauterine pressures during pushing than compared to nonobese (BMI < 35 kg/m2). This suggests that obese patients may need a longer second stage of labor or a longer duration of pushing to achieve vaginal birth.