Strengths and Limitations
This study has several limitations. Only cases of singleton pregnancies in which renal function tests were performed prior to delivery were included. The maternal renal function tests reviewed in this study were based on blood sample results taken closest to the time of delivery; however, most cases were tested only once, and data over time during pregnancy were not reviewed. Almost all blood tests were performed for maternal screening prior to cesarean section, resulting in earlier weeks in the twin pregnancy group. Cardiac output during pregnancy is reported to vary greatly with maternal posture and uterine size (e.g., amniotic fluid volume); however, there are no quantitative data on these factors. Lastly, we had no data regarding proteinuria (albuminuria) in this study. In future, we would like to examine albuminuria and cystatin C levels.