Objective We aimed to evaluate the differences in obstetrics and neonatal outcomes, such as mode of delivery, gestational diabetes mellitus, preeclampsia, and infant birth weight between pregnancies with normal and insufficient vitamin D levels. Methods The study was designed as a retrospective study. One hundred and seventy-nine pregnant women who were followed up at our clinic and whose vitamin D levels were evaluated in each trimester were included. All patients were administered 1200 IU/day beginning from the 12 weeks of gestation in accordance with the national guidelines. Vitamin D levels above 20 ng/ml were defined as sufficient, and those below 20 ng/ml were defined as insufficient. Results The median vitamin D level in the third trimester was significantly higher than that in the first and second trimesters (p<0.001). There was a moderate positive correlation between vitamin D levels in infant cord blood at the time of birth and vitamin D levels in the third trimester (p<0.001, R=0.496). Birth weights of the patients with insufficient vitamin D levels in the first trimester but with sufficient neonatal cord blood levels as a result of treatment were significantly higher compared to those in patients with insufficient cord blood vitamin D levels (3327 g vs. 3133 g, p=0.030). Conclusion This study observed that neonatal cord blood vitamin D level is a better indicator than antenatal vitamin D levels. Regardless of first-trimester vitamin D levels, infant birth weights were significantly higher in the group with sufficient neonatal cord blood levels.