<p>Background: There is a growing concern about the high prevalence of vitamin D deficiency and its relationship with variety of diseases worldwide. The objective of this study was to determine the prevalence of vitamin D deficiency and its relationship with pregnancy adverse effects in Yazd.<br /> Methods: This was a cross sectional study conducted among 200 nulliparous women from October 2013 to April 2014. Data containing socio-demographic and personal details, vitamin D level, pregnancy complications and growth situation of newborns were collected and analyzed using Mann-Whitney, Kruskal-Wallis and Pearson&rsquo;s correlation coefficient by SPSS. p&lt;0.05 was considered statistically significant.<br /> Results: The mean serum 1, 25 (OH)₂D₃ concentration was 20.3&plusmn;10.8<em> &micro;g/l</em>. Totally, 78% of the women had less than sufficient levels. Mean of vitamin D was significantly higher in natural or elective cesarean in comparison with abortion and emergency cesarean (p=0.040). Risk of abortion was 3.1(1.39-6.8) and higher in severely deficient group in comparison to women with vitamin D deficiency (p=0.017) and mean of vitamin D group was significantly lower in women who had oligohydramnios or polyhydramnios complication (p=0.045).<br /> Conclusion: The study findings revealed that vitamin D deficiency is prevalent in pregnant women and it is significantly associated with elevated risk for abortion, and oligohydramnios or polyhydramnios. Probably, a targeted screening strategy can be suggested to detect and treat women at high risk of vitamin D deficiency in early pregnancy as a simple way to reduce the risk of these adverse pregnancy outcomes in Yazd.</p>