Association of Unilateral Renal Agenesis With Adverse Outcomes in Pregnancy: A Matched Cohort Study

Background: Data regarding the effect of a solitary kidney during pregnancy have come from studies of living kidney donors. We evaluated the risk for adverse pregnancy outcomes in women with a single kidney from renal agenesis.

Study design: Matched cohort study.

Setting & participants: Using data from 7,079 childbirths from an integrated health care delivery system from 1996 through 2015, we identified births from women with renal agenesis. Only first pregnancies and singleton births were included. After excluding those with diabetes and kidney disease, 200 women with renal agenesis were matched 1:4 by age (within 2 years), race, and history of hypertension to women with 2 kidneys.

Predictor: Renal agenesis defined by International Classification of Diseases, Ninth Revision (ICD-9) codes prior to pregnancy.

Outcomes: The primary outcome was adverse maternal outcomes, including preterm delivery, delivery by cesarean section, preeclampsia/eclampsia, and hospital length of stay. Adverse neonatal end points were considered as a secondary outcome and included low birth weight (<2,500g) and infant death/transfer to acute inpatient facility.

Results: Mean gestational age at delivery was 37.9±2.1 weeks for women with renal agenesis compared to 38.6±1.8 weeks for women with 2 kidneys. Compared with women with 2 kidneys, those with renal agenesis had increased risk for preterm delivery (OR, 2.88; 95% CI, 1.86-4.45), delivery by cesarean section (OR, 2.11; 95% CI, 1.49-2.99), preeclampsia/eclampsia (OR, 2.41; 95% CI, 1.23-4.72), and length of stay longer than 3 days (OR, 1.81; 95% CI, 1.18-2.78). Renal agenesis was not significantly associated with increased risk for infant death/transfer to acute facility (OR, 2.60; 95% CI, 0.57-11.89) or low birth weight after accounting for preterm delivery (OR, 2.11; 95% CI, 0.76-5.88).

Limitations: Renal agenesis was identified by ICD-9 code, not by imaging of the abdomen.

Conclusion: Women with unilateral renal agenesis have a higher risk for adverse outcomes in pregnancy.