Background and aims Vitamin D deficiency during pregnancy has important health implications for the mother and infant. The aim of the present study was assess the effect of pre-pregnancy BMI on 25–hydroxyvitamin D [25(OH) D] concentrations.

Methods One hundred and eighty women aged between 19- 39 year, in a first trimester of pregnancy were enrolled serially from a referring university hospital in Tehran. Serum 25(OH) D was measured at the first trimester. The normal range for serum 25(OH) D was 25–125 nmol/L (10–50 ng/mL). Spearman rank correlation coefficient was used to test for correlations between pre-pregnancy BMI and serum 25 (OH) D levels.

Results Mean maternal serum 25(OH)D was 21.4 ±1.34 nmol/L. The prevalence of hypovitaminosis [25(OH) D ≤ 25 nmol/L] was 62.4%. In this study half of the participant had BMI >30 kg/m² and the others had BMI <30 kg/m². Almost forty percentage (38%) of women with a pre-pregnancy BMI >30 and 24.4% BMI <30 had vitamin D deficiency. Hypovitaminosis D was independently associated with conception of dairy, eggs, fish <twice a week. There was no significant association between vitamin D deficiencies, parity, gravity, age was seen. There was a moderate, negative correlation between pre pregnancy BMI and serum 25(OH) D in first trimester (r = -0.38; p < 0.001).

Conclusion These findings support the need to balance pre-pregnancy weigh to decrease the risk of mother and infant health complications and higher-dose supplementation is needed to improve maternal and neonatal vitamin D nutriture.