Kidney function and future risk for adverse pregnancy outcomes: a population-based study from HUNT II, Norway

Background. Current knowledge on prepregnancy reduced kidney function and the risk of adverse pregnancy outcomes mainly relies on small studies in selected populations. We aim to investigate whether reduced kidney function is associated with the risk of adverse pregnancy-related outcomes in the general population. Methods. A population-based study linking all women attending the Second Health Study in Nord-Trondelag, Norway (1995-97) and subsequent pregnancies registered in the Medical Birth Registry. Multivariable random-effect logistic regression analysis was used to explore the association between renal function and study outcome. Results. The mean eGFR among 3405 women was 107.6 +/- 19.4 ml/min/1.73 m(2) at baseline; 18.8% and 0.1% had eGFR of 60-89 and < 60, respectively. Over the next 11 years, they gave birth to 5655 singletons of whom 885 (17.7%) were complicated with preeclampsia, small for gestational age (SGA) or preterm birth. Women with eGFR 60-89 were not at increased risk for this combined outcome compared to women with eGFR >= 90, although women with eGFR 60-74 tended to have an increased risk. Neither was reduced kidney function a risk factor among women with microalbuminuria, but those with an eGFR of 60-89 plus hypertension had a significantly increased risk: odds ratios for preeclampsia, SGA or preterm birth were 2.58 (95% CI 1.40-4.75, P < 0.001) and 10.09 (95% CI 2.38-42.87, P < 0.001) in hypertensive women with eGFR 75-89 and 60-74, respectively. Relative excess risk due to interaction between reduced kidney function and hypertension was 2.23 (95% CI 1.35-3.10, P < 0.001). Women with a reduced kidney function were not at increased risk for other pregnancy complications like caesarean section, maternal bleeding, dystocia, pre-labour rupture of membranes, Apgar score <= 7, stillbirth or congenital malformations. Conclusions. Women with eGFR 60-89 ml/min/1.73 m(2) were not at increased risk for preeclampsia, SGA or preterm birth unless they were also hypertensive.