Background and Purpose: Maternal Vitamin D deficiency is a global public health problem. The main objective of this prospective cohort study is to assess the independent effect of maternal 25-hydroxyvitamin D levels in early pregnancy on the risk of GDM and PIH. Methods: 574 nulliparous mothers with singleton pregnancies attended the antenatal out-patient department of our institution during the study period from July 2013 to June 2014 and were selected after taking proper history and investigations. In the first visit, Vitamin D estimation was done by HPLC method along with other routine investigations. Vitamin D deficient mothers, i.e. serum 25-hydroxyvitamin D<50 nmol/L(20 ng/ml) were taken as exposed and other mothers as non-exposed and followed upto term to study the development of GDM and PIH in the index pregnancy. Only mothers attending OPD on Wednesday were included in our study. Results: Out of 574 mothers, 375(65.3%) were vitamin D insufficient, 47(8.2%) developed GDM and DGGT, and 57(9.9%) developed PIH in third trimester. A significant positive association between low 25(OH) D levels and an increased risk of GDM(p=.01) and PIH(p=.049) was found in our study. A correlation between obesity, maternal vitamin D status and subsequent development of GDM and PIH was also illustrated but were statistically insignificant. Conclusion: Hypovitaminosis D during pregnancy and its undesirable health outcomes is an area of growing concern. As maternal obesity rates increase and incidence of GDM also rises, it is becoming increasingly important to understand modifiable risk factors as vitamin D status. Ultimately, RCTs will be needed to test if vitamin D supplement affects GDM and PIH risk and improves maternal and perinatal outcomes.