Purposes To analyze the effects of vitamin D deficiency in pregnant women on common adverse pregnancy outcomes and small for gestational age (SGA) and to detect the expression of inflammatory factors in pregnant women to provide a theoretical basis for the treatment of vitamin D deficiency in pregnant women. Methods Serum samples from pregnant women from January 2015 to December 2015 were collected to measure the 25-(OH)D level. The effects of maternal age, pregnancy, season, parity and temperature on vitamin D levels in pregnant women were recorded. Then, the relationship between vitamin D levels and gestational diabetes mellitus, gestational hypertension, premature rupture of membranes, cesarean section, premature delivery and spontaneous abortion, and neonatal gestational age were analyzed. The expression of IL-6 and TNF-α in serum was detected by RT-PCR and western blot. Results The incidence of vitamin D deficiency, insufficiency and sufficiency in pregnant women in this region was 83.28%, 15.36% and 1.36%, respectively. Age, pregnancy, sampling season and parity were the influencing factors on vitamin D level, and multivariate logistic regression analysis showed that summer, autumn and temperature were protective factors for adequate vitamin D in pregnant women (P <0.05). Vitamin D levels in pregnant women were associated with preterm birth, spontaneous abortion and SGA. The incidences of preterm birth, spontaneous abortion and SGA were higher in the vitamin D deficiency group (P<0.05). ConclusionThe serum vitamin D level of pregnant women in this area is low and is affected by multiple factors such as age, pregnancy, season, parity and temperature. Low vitamin D levels can increase the risk of premature birth, spontaneous abortion and SGA in pregnant women, and its low expression is common. As it also leads to inflammation, increasing the level of vitamin D in the serum of pregnant women can effectively reduce the occurrence of related diseases.