Chronic kidney disease (CKD) is a global health issue [1]. The incidence of CKD in women of childbearing age is estimated to be 0.1–4% [2]. Approximately 1 in 750 pregnant women are with stage 3–5 CKD, which is linked to adverse pregnancy outcomes, including preterm birth, fetal growth restriction and a decline in maternal renal function.

Many studies performed over the last few decades have indicated that patients with mild renal functional impairment usually have acceptable pregnancy outcomes and that pregnancy does not have an obvious effect on glomerular filtration rate (GFR) deterioration [3], [4], [5], [6], [7]. However, information on pregnancy outcomes among patients with moderate to severe renal impairment (stage 3–5 CKD) is still scant. Many studies have revealed that adverse pregnancy outcomes are determined not only by the GFR but also by the presence of proteinuria and chronic hypertension [4], [8]. A recent study[9] reported on neonatal and maternal outcomes of pregnancies in women with stage 3–5 CKD and found that chronic hypertension, pre- or early pregnancy proteinuria and a gestational fall in serum creatinine of <10% of pre-pregnancy values are more important predictors of adverse obstetric and renal outcomes than GFR; however, in this study, preeclampsia was not set as an adverse pregnancy outcome, and the effect of low-dose aspirin (LDA), which is now widely used in patients with CKD for preeclampsia prophylaxis, on adverse pregnancy outcomes was not analyzed. Patients with low GFR and proteinuria have a higher likelihood of developing superimposed preeclampsia, which may have adverse effects on pregnancy and long-term renal outcomes [10]. Furthermore, although we know that advanced renal disease, proteinuria and chronic hypertension are predictors of adverse pregnancy outcomes, the interplay between these predictors and adverse pregnancy outcomes remains unclear, limiting the information available for counseling prior to or early in pregnancy.

The aims of this study are (1) to identify the relationship between prognostic predictors and adverse pregnancy outcomes; specifically, we want to shed light on the impact of early-pregnancy renal function and proteinuria levels on pregnancy outcomes while considering the presence of hypertension during pregnancy and (2) to investigate whether pregnancy may accelerate the estimated GFR (eGFR) reduction of patients with stage 3–5 CKD.