Is renal hyperfiltration protective in chronic kidney disease-stage 1 pregnancies? A step forward unravelling the mystery of the effect of stage 1 chronic kidney disease on pregnancy outcomes.

BACKGROUND: The correlation between advanced or proteinuric chronic kidney disease (CKD) and adverse pregnancy outcomes is intuitive, although how early CKD affects pregnancy remains unknown. Glomerular hyperfiltration is a physiological response to pregnancy, correlated with outcomes in hypertension or collagen diseases. The aim of the study was to correlate first trimester hyperfiltration with pregnancy outcomes in stage 1 CKD patients.

METHODS: A historical prospective study was conducted on the database of our Unit, gathering all pregnant CKD patients referred since 1 January 2000. From 383 pregnancies referred in 2000-2013, 75 patients were selected (stage 1 CKD, referred within the 14th gestational week, singleton deliveries, absence of diabetes, hypertension or nephrotic proteinuria at referral, body mass index [BMI] < 30); 267 'low-risk' pregnancies, followed in the same setting, served as controls. Glomerular filtration rate (GFR) was assessed by Chronic Kidney Disease Epidemiology Collaboration (CKD-EPI) and dichotomized at 120 mL/min. The odds for Caesarean section, prematurity, need for Neonatal Intensive Care Unit (NICU) were assessed by univariate analysis and logistic regression.

RESULTS: Risk for adverse pregnancy outcomes was not affected by hyperfiltration (univariate OR GFR ≥ 120 mL/min: Caesarean section 1.30 (0.46-3.65); preterm delivery: 0.84 (0.25-2.80)). In contrast, even in these cases with normal kidney function, stage 1 CKD was associated with prematurity (17.3% vs 4.9% P = 0.001), lower birth weight (3027 ± 586 versus 3268 ± 500 P < 0.001) need for NICU (12% vs 1.1% P < 0.001). In the multivariate analysis, the risks were significantly increased by proteinuria and maternal age but not by GFR.

CONCLUSIONS: In pregnant Stage 1 CKD patients, hyperfiltration was not associated with maternal-foetal outcomes, thus suggesting a need to focus attention on qualitative factors, eventually enhanced by age, as vascular stiffness, endothelial damage or oxidative stress.