Participants
This was a retrospective study of 2676 deliveries at our institution from January 2019 to June 2021. In our hospital, when a cesarean section was necessary (or is considered highly likely), we performed blood tests (complete blood counts, biochemical tests including kidney and liver function, coagulation tests, and tests for infectious diseases including HIV), chest radiography, and electrocardiography as preoperative tests, within at least one month of delivery. All twin pregnancies underwent preoperative examinations. After excluding 965 patients (including 959 cases in which blood tests were not performed, three cases of missing data, and three cases of triplet pregnancy), we finally enrolled 1711 patients pregnant with 1547 singleton pregnancies and 164 twin pregnancies who underwent renal function tests (serum blood urea nitrogen [BUN], creatinine, and estimated glomerular filtration rate [eGFR]) within at least one month of delivery (Supplementary Figure 1). The study conformed to the principles outlined in the Declaration of Helsinki of 1964. This study was approved by the Ethics Committee of the Japanese Red Cross Nagoya Daiichi Hospital, Nagoya, Japan (approval number: 2021-422).