This retrospective cohort study investigated the association between ultrasonographic estimated fetal weight (EFW) and adverse maternal and neonatal outcomes after vacuum-assisted delivery (VAD). It included women with singleton pregnancies at 34−41 weeks gestation, who underwent ultrasonographic pre-labor EFW and VAD in an academic institution, over 6 years. Adverse neonatal and maternal outcomes included shoulder dystocia, clavicular fracture, or third- and fourth-degree perineal tears. A receiver−operator characteristic curve was used to identify the optimal weight cut-off value to predict adverse outcomes. Fetuses above and below this point were compared. Multivariate analysis was used to control for factors that could lead to adverse outcomes. Eight-hundred and fifty women met the inclusion criteria and had sonographic EFW within two-weeks before delivery. Receiver−operator characteristic curve analysis found that ultrasonographic EFW 3666 g is the optimal threshold for adverse outcomes. Based on these results, outcomes were compared using EFW 3700 g. The average EFW in the ≥3700 g group (n = 220, 25.9%) was 3898 ± 154 g (average birthweight 3710 ± 324 g). In the group <3700 g (n = 630, 74.1%), average EFW was 3064 ± 411 g (birthweight 3120 ± 464 g). Shoulder dystocia and clavicular fractures were more frequent in the higher EFW group (6.4% and 2.3% vs. 1.6% and 0.5%, respectively; p < 0.05). Women in the ≥3700 g group experienced more third- and fourth-degree perineal tears (3.2% vs. 1%, p = 0.02). Multivariate logistic regression analysis found maternal age, diabetes and sonographic EFW ≥ 3700 g as independent risk-factors for adverse outcomes. Sonographic EFW ≥ 3700 g is an independent risk-factor for adverse outcomes in VAD. This should be considered when choosing the optimal mode of delivery.
Keywords: estimated fetal weight; shoulder dystocia; third- and fourth-degree perineal tears; vacuum-assisted delivery.