Unilateral renal agenesis has an incidence of 1:2,300 individuals. Patients with unilateral renal agenesis are at increased risk for development of proteinuria, hypertension, and renal insufficiency. A recent systematic review found that 10% of individuals with unilateral renal agenesis had a GFR less than 60 and 21% had microalbuminuria. The hyperfiltration hypothesis proposed by Brenner et al is typically used to explain these findings. As hyperfiltration occurs as a physiologic response in normal pregnancies, it is important to consider whether a woman with unilateral renal agenesis may be at increased risk for adverse outcomes during pregnancy.
A recent study published in AJKD by Kendrick et al examines pregnancy outcomes in pregnant women with unilateral renal agenesis. Using ICD-9 codes, the authors identified primiparous women with unilateral renal agenesis and singleton pregnancies from 1999-2015 in the Intermountain Healthcare system (which serves Idaho and Utah). Women with a pre-pregnancy diagnosis of diabetes or chronic kidney disease (CKD) were excluded from the analysis. CKD was also defined by ICD-9 code and included the code for proteinuria. Matched controls were created in a 1:4 ratio to women with 2 kidneys by age at delivery, race, and history of chronic hypertension. Baseline characteristics of the groups are shown below:
A total of 200 women with unilateral renal agenesis were matched with 800 women with 2 kidneys. The primary outcome of this study was adverse maternal outcomes including 1) preterm delivery, 2) need for cesarean section, 3) maternal hospital stay longer than 3 days, and 4) a preeclampsia/eclampsia diagnosis. Secondary outcomes were adverse neonatal outcomes that were defined as 1) low infant birth weight and 2) a combined outcome of infant death and/or infant transfer to an acute inpatient facility.
As seen in Table 2 below, maternal unilateral renal agenesis was associated with an increased risk of all the studied adverse maternal outcomes as well as an increased risk of low infant birth weight.
This study clearly demonstrates the risk of pregnancy in subjects with unilateral renal agenesis. The results are consistent with other studies that have shown an increased risk of adverse pregnancy outcomes in women with mild CKD as well as women who have previously donated a kidney. There are limitations to the study, thus we should interpret the results carefully. ICD-9 codes can be an insensitive measure for CKD, so it is plausible that women with significantly reduced GFRs were included in the study, skewing the results. The study population of mostly Caucasian women in Idaho and Utah also make these results difficult to generalize. Interestingly, high altitude (as in Idaho and Utah) has been linked with an increased risk for preeclampsia and impaired fetal growth as well.
This Kendrick et al study, combined with the rest of the mounting evidence that women with even mild CKD have an increased risk of adverse pregnancy outcomes, provides clinicians more data to use when counseling a woman with renal agenesis without significant CKD on her risks of pregnancy.
Title: Association of Unilateral Renal Agenesis With Adverse Outcomes in Pregnancy: A Matched Cohort Study
Authors: J. Kendrick, J. Holmen, Z. You, G. Smits, and M. Chonchol