In order to investigate the influence of delivery mode on biological inactive renin levels in fetal circulation, plasma inactive renin (PIR), plasma renin activity (PRA) and plasma total renin (PTR) were measured in umbilical venous blood samples of 21 infants delivered vaginally after spontaneous labor and of 9 infants delivered by elective cesarean section after the onset of labor. Biological renin activities were measured by bioassay. The PIR levels in infants delivered vaginally were significantly lower than those in infants delivered by cesarean section, while the PRA levels were the opposite. However, the PTR levels were not significantly different between the two groups. These results suggest that the plasma levels of biological inactive renin in infants delivered vaginally may decrease, probably due to its conversion to active renin in the second stage of labor.

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Background Pregnant women with no risk factors should have received elective CS later than 37 weeks because the the incidence of respiratory disorder of neonates decreases [5-8]. Hence, the appropriate timing that CS for placenta previa was performed on the side of both the mother and neonate was unclear. This study aimed to evaluate the most appropriate timing of cesarean section (CS) in placenta previa cases. Methods Singleton pregnant women who were scheduled to undergo an elective CS at 36 weeks (Group A) or 37 weeks of gestation (Group B) for placenta previa between August 2003 and July 2018 at our hospital were identified. The timing of CS was decided based on the judgment of the doctor with consideration of the risk of bleeding or faculties adaptation. Maternal and neonatal outcomes between both groups were retrospectively examined. Results There were a total of 272 cases, with 76 cases assigned in Group A and 196 cases in Group B. There was no difference in emergency CS rate (p = 0.36), intraoperative hemorrhage (p= 0.86), total hemorrhage at delivery (p= 0.64), and additional treatment between Group A and Group B. The birth weight of neonates in Group A was smaller (p < 0.001) compared to those in Group B. Apgar scores of neonates at 1 minute (p = 0.04) and 5 minutes (p < 0.01) were lower in Group A than in Group B. Furthermore, neonatal hypoglycemia was higher in neonates of Group A (p < 0.02). Conclusions Regardless of selection bias, there were no merits to perform CS for placenta previa at 36 gestational weeks on both mother and neonate sides. Further studies are required to evaluate when elective CS for placental previa should be scheduled.