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Labor arrest is the most common indication for emergency cesarean section (ECS). Increased biparietal diameter (BPD) has been reported as a risk factor for ECS due to labor arrest in different countries, but it is unclear whether this relationship is relevant in Japan. Considering the difference in maternal physique according to race and ethnicity, we retrospectively evaluated the association between ECS due to labor arrest and BPD, measured by ultrasonography < 7 days before term deliveries in Japanese women. BPD is routinely measured in Japan for estimating fetal weight. Information was extracted from obstetric records at the National Hospital Organization Kofu National Hospital between January 2012 and November 2019. Patients with multiple pregnancies, instrumental (forceps or vacuum) delivery, elective cesarean sections, and ECS due to reasons other than labor arrest were excluded. Thus, 2,695 women were included (age, 31.3 ± 6.2 years; pre-pregnancy body mass index, 20.9 ± 3.2 kg/m 2 ), and 1,319 (48.9%) were nulliparous. The incidence of ECS due to labor arrest was 2.4% (64/2,695). Multivariable analysis indicated that BPD was significantly associated with ECS due to labor arrest (adjusted odds ratio, 1.12; 95% confidence interval, 1.04-1.20). The optimal BPD cut-off value for predicting ECS due to labor arrest was 94 mm (area under the curve, 0.61; sensitivity, 53.1%; specificity, 65.1%). Despite the significant association with ECS, BPD is not useful to predict ECS due to labor arrest. Thus, mothers should be encouraged for attempting vaginal deliveries, even in the case of having babies with large fetal BPD.