Association Between Maternal Vitamin D Levels During Pregnancy And Small For Gestational Age Infants: A Population-based Birth Cohort Study

ObjectiveTo describe the maternal vitamin D levels in the first,second,and third trimester of pregnancy in Ma’anshan city,and examine the risk factors of small for gestational age(SGA)infants,explore the relationship between vitamin D levels and SGA infants.MethodsAccording to inclusion and exclusion criteria,3,265 pregnant women from Ma’anshan Birth Cohort were enrolled in the present study between May 2013 and September 2014.In the first(<14 weeks),second(24-28 weeks),and third(32-36 weeks)trimester of pregnancy,the sociodemographic information,related factors,and lifestyle of all pregnant women were coolected with a self-designed questionnaire.And information on gestational age at birth,mode of delivery and the birth weight,length and head circumference of newborns were collected during childbirth from the delivery.At the same time,in the first,second,and third trimester of pregnancy,the blood samples of pregnant women were collected and the vitamin D concentration was examined by radioimmunoassay(RIA).The Chi-square test and Multinomial logistic regression model were used to analyze the risk factors of SGA.According to the Institute of Medicine(IOM)standards,we categorized the vitamin D levels as three groups:vitamin D deficiency(as reference),vitamin D insufficiency,and vitamin D sufficiency.Multinomial logistic regression models were used to explore the effect of vitamin D levels on the risk of SGA infants.ResultsA total of 3,265 mother-and-singleton-offspring pairs were enrolled in the present study.In the first trimester of pregnancy,reliable serum vitamin D levels was measured in3,070 of these pregnant women,the mean levels were 18.22±8.39 ng/ml,and the prevalence of vitamin D deficiency was 66.1%.In the second trimester of pregnancy,reliable serum vitamin D was measured in 3,088 of these pregnant women,the mean levels were 22.76±10.43 ng/ml,and the vitamin D levels of 46.5%of the pregnant women were deficient.In the third trimester of pregnancy,serum vitamin D levels were measured in 2,931 of these pregnant women,the mean levels were 20.06±10.25ng/ml,and the rate of vitamin D deficiency was 59.2%among the pregnant women.At the same time,compared to pregnant women which were sampled in summer,the vitamin D levels were markedly higher in winter and spring.The results of Multinomial logistic regression analysis showed that pre-pregnancy body mass index(BMI)<18.5 kg/m~2,hypertensive disorder complicating pregnancy,and living in rural areas were risk factors for SGA infants.Multinomial logistic regression also showed that,compared with vitamin D deficiency group,vitamin D insufficiency(OR=1.11,95%CI:0.84-1.46)and vitamin D sufficiency(OR=0.99,95%CI:0.70-1.41)were not associated with SGA in the second trimester of pregnancy,similarly,vitamin D insufficiency(OR=1.09,95%CI:0.80-1.48)and vitamin D sufficiency(OR=1.13,95%CI:0.77-1.66)also were not related with SGA infants in the third trimester of pregnancy.However,we found that there was a correlation between vitamin D insufficiency and SGA infants(OR=0.72,95%CI:0.52-0.99,P=0.048).In general,only in season of summer-autumn,vitamin D insufficiency in the first trimester of pregnancy can decrease the risk of SGA infants compared with vitamin D deficiency group(OR=0.56,95%CI:0.37-0.86,P=0.008),this correlation was not found in season of winter-spring.Vitamin D levels in the second and third trimester of pregnancy were not associated with SGA infants both in season of summer-autumn and winter-spring(P>0.05).ConclusionsIn the present study,the prevalence of vitamin D deficiency in the first and third trimester of pregnancy were higher than in the second trimester of pregnancy,and vitamin D levels were markedly higher in summer-autumn than in winter-spring.We found that here was a correlation between vitamin D insufficiency and the risk of SGA in the first trimester of pregnancy,and this association was only found in season of summer-autumn.This study did not find the correction between vitamin D levels and the risks of SGA infants in the second and third trimester.