Urinary thiosulfate level in pregnant women

Renal colic is the most common cause of non-obstetric hospitalization in pregnant patients. Prior study has established increased excretion of inhibitors of calcium salt crystallization in pregnancy. This phenomenon is thought to be a physiological protective mechanism against urolithiasis promoters. Thiosulfate is a compound reported to have a protective effect against calcium stone formation and urinary excretion of thiosulfate and has been reported to increase during pregnancy. Our study measured urinary thiosulfate on a controlled diet during the third trimester and the post-partum period and sought to assess whether thiosulfate serves as a viable lithogenic protective agent.

We recruited a cohort of pregnant patients and obtained 24-hour urine collections on a standardized diet in the third trimester and again 6 weeks post-partum.

A total of 14 pregnant women submitted urine samples for the analysis of urinary thiosulfate in the third trimester. 24-hour urine samples were collected during the third trimester, post-partum, and post-lactation stages. A total of 4 patients had new stone formation during pregnancy. There was no statistical difference (p = 0.62) of urinary thiosulfate across the third trimester (12.1 µmol/day, interquartile range (IQR) 9.1 - 19.7), post-partum (11.1 µmol/day, IQR 8.8 - 17.4), and post-lactation (16.1 µmol/day, IQR 8.2 - 25.2) stage. Stratified analysis showed no statistically significant difference in thiosulfate level between stone formers vs. non-stone formers.

Endogenous urinary thiosulfate does not change significantly from the third trimester of pregnancy to post-partum in our cohort of patients on a standardized diet. Our observation does not support urinary thiosulfate as a lithogenic protective factor augmented during pregnancy.