Which way is better to deliver the very heavy baby: mode of delivery, maternal and neonatal outcome

Purpose: Currently there are no existing data regarding the maternal and neonatal outcomes for nulliparous women delivering neonates with birthweight above 4500 g. We aim to evaluate birth outcome among these subset of parturients. Methods: A retrospective study of nulliparous delivering a singleton fetus weighing ≥ 4500 g in two tertiary medical centers between 2007 and 2018. Women who chose to undergo a trial of labor (TOL) were compared to those who underwent elective cesarean delivery (CD). Results: Overall, 121 women were included. Seventy eight (65.4%) women elected a TOL while 43 (34.6%) had elective CD. Of women who chose TOL, 46 (59%) delivered with unassisted vaginal delivery, 28 (36%) by intrapartum CD, and 4 (5%) by assisted vaginal delivery, reaching TOL success rate of 64% (50/78). The rates of shoulder dystocia and anal sphincter injury in vaginal deliveries were 5/50 (10%) and 2/50 (4%) respectively. Successful TOL was negatively associated with the presence of gestational diabetes [5 (18%) vs. 0 (0%), OR 0.8 (95% CI 0.7–0.9), p = 0.005], and was positively associated with maternal height (median 170 cm vs. 165 cm, p = 0.002), epidural analgesia [42 (84%) vs. 16 (57%), OR 3.5 (95% CI 1.2–9.8), p = 0.009] and spontaneous onset of labor (38 (76%) vs. 10 (36%), OR 5.7 (95% CI 2.1–15.6), p = 0.001. Neonates born after TOL were more commonly complicated by meconium aspiration syndrome as compared to no TOL (9 (11%) vs. 0 (0%), OR 1.1 (95% CI 1.04–1.22, p = 0.02). Only maternal height was independently associated with successful TOL (aOR 6.9 (95% CI 1.03–46.3, p = 0.04). Maternal and neonatal adverse composite outcomes were associated with gestational hypertensive disorders (10 (50%) vs. 5 (5%). OR 19.2 (5.5–67.4), p < 0.001) and with delivery before 40 weeks (9 (57%) vs, 86 (82%), OR 3.5 (95% CI 1.2–10.6, p = 0.02), respectively. Conclusions: Trial of vaginal delivery in nulliparous with fetuses ≥ 4500 g was associated with a high failure rate, with only two thirds of parturients achieving successful vaginal delivery. Nevertheless, neonatal outcomes mostly did not differ according to the mode of delivery. Maternal height was the only factor associated with successful vaginal delivery.