Introduction: Pregnancy is associated with an increased lifetime prevalence of nephrolithiasis. During pregnancy, purported changes in urinary milieu include hypercalciuria and alkaline urine pH, which may predispose to calcium phosphate (CaPhos) urolithiasis. Postpartum, it is unknown whether the cumulative number of pregnancies is associated with persistent risk of these findings and CaPhos stone formation. We studied the effect of prior pregnancies on the urinary milieu and stone composition in a cohort of female stone formers.
Methods: With IRB approval, a single-center retrospective review of stone patients treated between 2007 and 2017 was performed. The subjects identified were non-cystinuric, living female patients with complete 24-hour urinalysis and available stone analyses who consented to pregnancy history phone questionnaire. Linear regression and t-test were used to assess the association of CaPhos supersaturation (SSCaP) and pH between nongravid (G0) and previously gravid women. Age, body mass index (BMI), diabetes, and gout were adjusted for in the multivariate analysis.
Results: Of 116 who met inclusion criteria, 22 (19%) were G0 and 94 (81%) were previously gravid. Of those previously gravid, 15 (12.9%) were primigravid (G1), 26 (22.4%) were secundigravid (G2), and 53 (45.7%) had three or more pregnancies (G3+). Mean age was 54.3 years and did not differ significantly by history of pregnancy (p = 0.9). Mean years since last pregnancy was 24.6. Mean BMI at the time of 24-hour urine was 29.6 kg/m2. Previously gravid women were more likely to have hypercalciuria than G0 women (50% vs 22.7%, p < 0.05). Urine calcium was significantly increased in G3+ women compared to G0 women (211.9 mg/day vs 153.2 mg/day, p < 0.05). On multivariate analysis, both SSCaP and urine calcium remained elevated in G3+ women compared to G0 women (+0.49 and +51.2 mg/day, respectively, p < 0.05). Prior gravidity did not impart a significant effect on the most recent urine pH, however. Ultimately, G3+ women were more than thrice as likely to have CaPhos-containing stones at a mean 22.9 years after pregnancy compared with G0 women (OR 3.7, p < 0.05).
Conclusions: Women with multiple pregnancies were significantly more likely than G0 women to exhibit hypercalciuria and elevated SSCaP, even decades after their last pregnancy, suggesting the possibility of lasting effects on the urinary milieu. Furthermore, the increased likelihood of CaPhos stones among multigravids suggests these 24-hour urinary differences may be clinically relevant. These findings may help further unravel gender-based differences in nephrolithiasis. Source of