Maternal Renal Function During Pregnancy and the Early Postpartum Period in Normotensive and Hypertensive Pregnancies.

AIM: We aimed to assess renal function trends during pregnancy and the early postpartum period and establish trimester-specific reference ranges for maternal renal function parameters in Japan, including comparisons with pregnancies complicated by hypertensive disorders of pregnancy (HDP) and preeclampsia. METHODS: This multicenter retrospective study used data collected from 12 primary maternity care units in Japan between 2011 and 2018. Serum creatinine and blood urea nitrogen (BUN) levels were analyzed from early pregnancy to postpartum Day 7 in 17 460 women with uncomplicated term pregnancies (370/7-416/7 weeks of gestation) and 1460 women with HDP. Additionally, 17 460 non-pregnant women matched for age, body weight, and height were included in the study. RESULTS: Serum creatinine and BUN levels were lower in women with uncomplicated pregnancies than in non-pregnant women and reached their lowest levels in the second trimester. The 97.5th percentile serum creatinine value was 0.52 mg/dL in the second trimester, compared with 0.82 mg/dL in non-pregnant women. The median serum creatinine levels in uncomplicated pregnancies were approximately 30% lower than those in non-pregnant women. Serum creatinine levels began to normalize during the postpartum period but did not return to baseline non-pregnant status by Day 7. In women with HDP and preeclampsia, serum creatinine levels increased in the late third trimester and peaked on postpartum Day 1; in 7.0% of women with preeclampsia, they exceeded 1.0 mg/dL. CONCLUSION: We determined reference ranges for maternal renal markers in a Japanese cohort study. Maternal renal function shows dynamic alterations from the non-pregnant state through pregnancy to the postpartum period.