Japanese parturient body mass index and the role in initial nerve block height of women undergoing cesarean delivery with spinal anesthesia

The present retrospective cohort study was designed to determine body mass index (BMI) at the delivery in women undergoing cesarean section in a Japanese urban area, and whether the nerve block height after spinal anesthesia upon the cesarean delivery relates to the lower maternal BMI, less gestational age, or underweight fetus at birth in the population. A total of 401 pregnant women undergoing cesarean delivery with spinal anesthesia were evaluated retrospectively. We examined background differences, including BMI at the delivery, gestational age, and fetal birth weight between the cases with and without the adequate initial nerve block height less than the sixth thoracic vertebral level (Th6) after the spinal dose administration. The data demonstrated advanced maternal age pregnancy (median 35.5 years) and normal BMI (median 24.7) at the delivery in the population. The patients with the inadequate initial nerve block height immediately after the spinal dose administration documented significantly lower block height compared with those with adequate block height (Th8 [n = 55] vs Th4 [n = 346], P < 0.001). There was a risk of the low initial block height caused by either preoperative BMI <23, gestational age <37 weeks, or fetal birth weight <2500 g in the population. In a Japanese urban area, parturient median BMI undergoing cesarean delivery is in the normal range. Such lower BMI, in addition to less gestational age or underweight fetus, seems one of the factors causing the low initial block height upon spinal anesthesia.