Second Trimester Kidney Function and Adverse Pregnancy Outcomes among Patients with Lupus.

Key Points: In our combined cohort, second trimester kidney function was associated with adverse outcomes for patients with lupus. Measurement of kidney function during pregnancy may have potential benefit, especially among patients without kidney disease.

Background: Kidney function is not routinely assessed during pregnancy. Several studies have proposed antepartum kidney function, particularly second trimester kidney function, as a potential predictor of adverse pregnancy outcomes. It has been previously established that patients with systemic lupus erythematosus are at increased risk for adverse pregnancy outcomes. The association between second trimester kidney function and adverse pregnancy outcomes has not been evaluated in diverse patient populations, particularly among patients with high obstetrical risk.

Methods: In this observational study of pregnant patients with lupus in North America and Europe from 1995 to 2017, we used second trimester creatinine and eGFR to model the log odds of preeclampsia, preterm birth, low birthweight, fetal loss, and a composite of those outcomes. We incorporated these measures into a regression setting using fractional polynomials, and we further examined discrete formulations of eGFR.

Results: Among 684 pregnancies in patients with lupus, the mean second trimester creatinine was 0.63 mg/dl ±SD 0.26 and the median value 0.60 (interquartile range, 0.50–0.70). At least 1 in 3 patients in this combined cohort experienced an adverse outcome. Mixtures of U-shaped and linear relationships between continuous kidney function and the log odds of adverse pregnancy outcomes were observed. Stratifying the cohort by diagnosis of lupus nephritis (LN; active or in remission) or without diagnosis of nephritis, we found differences in the relationship between kidney function and adverse outcomes.

Conclusions: We observed high rates of adverse pregnancy outcomes in our diverse patient population comprised of pregnant patients with lupus with and without LN. We identified complex relationships between second trimester kidney function and adverse pregnancy outcomes that differed by the outcome and diagnosis of LN.