The Correlation Between Serum Vitamin D and Urinary Tract Infection in Pregnant Women: A Case–Control Study from Iran

Background Vitamin D deficiency is a common global health concern, particularly among pregnant women. It has been linked to various adverse maternal outcomes such as preterm birth, gestational hypertension, and increased susceptibility to infections. Urinary tract infection (UTI) is one of the most frequent bacterial infections during pregnancy, posing significant risks to both mother and fetus. This study aimed to investigate the association between serum vitamin D and UTI in Pregnant Women. Methods The case-control study conducted, 70 pregnant women were selected using convenience sampling in 2023–2024. Then they were divided into two groups, UTI and non-UTI. Both groups were matched on by one. The data were collected using a demographic information questionnaire and researcher-made checklist. After obtaining consent from participants, blood samples were collected using the peripheral venous catheter. Then the ELISA test was used to measure vitamin D in participants. Data were analyzed by SPSS version using, 26, applying chi-square, t-test, and logistic regression, with p < 0.05 considered significant. Results The mean serum vitamin D level was significantly lower in the UTI group (18.5 ± 6.1 ng/mL) compared with the control group (35.2 ± 9.5 ng/mL; p < 0.001). Vitamin D deficiency was observed in 82.9% of women with UTI versus 45.7% in controls. Logistic regression revealed that vitamin D deficiency increased the odds of UTI by 3.5 times (OR: 3.52; 95% CI: 1.42–8.70). Age, parity, and frequency of sexual intercourse were also associated with higher UTI risk. Conclusions Low Vitamin D levels are significantly associated with an increased risk of urinary tract infection during pregnancy. Routine screening and timely supplementation may reduce maternal morbidity and improve pregnancy outcomes.