Objective Our aims were to evaluate whether there is an inverse association between body mass index (BMI) and umbilical artery pH and to investigate the contribution of intraoperative hypotension on the umbilical artery pH. Study Design We conducted a retrospective cohort study of all women with a nonanomalous singleton at 37 to 41 weeks who underwent a scheduled cesarean delivery under spinal anesthesia at our facility from January 2006 to March 2012. The primary outcome was the proportion of patients in each BMI category with arterial cord pH < 7.10. Intraoperative blood pressure data were compared across BMI categories. Results In total, 717 mother-infant pairs met enrollment criteria. Mean arterial pH was significantly lower in women with elevated BMI (p = 0.014), notably with BMI ≥ 40 kg/m2. Baseline blood pressure increased linearly with increasing BMI (p < 0.001), however, so did the maximum drop in all blood pressure parameters (p < 0.001). After adjusting for potential confounders, including blood pressure, there was no longer an association between cord pH and BMI (p = 0.72). Conclusion For women undergoing a scheduled cesarean delivery under spinal anesthesia, umbilical artery pH is lower in women with BMI ≥40 kg/m2. Relative hypotension after spinal anesthesia is more pronounced with increasing BMI and may explain this effect.
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