| Backgrounds and ObjectivesPreterm birth(PTB)is defined as birth occurring before 37 weeks of pregnancy and more than 28 weeks.Preterm birth is the leading cause of neonatal mortality.In addition,preterm birth would increase the risk of growth and developmental disorders in children,especially the risk of neurodevelopmental disorders.The cause of preterm birth and specific biological mechanisms is often not known.The etiology of preterm labor is multifactoral,the most common risk factors include infections and inflammation.Vitamin D may increase the risk of preterm birth through regulating immune function and inflammatory cytokines.Findings from epidemiological studies concerning the association of maternal hypovitaminosis D during pregnancy and PTB yielded mixed results,and most were cross-sectional studies.Few of studies focus on different time point during pregnancy.We took Ma’anshan Maternal and Child Healthcare Hospital as the research field to investigate the prevalence of three trimester vitamin D deficiency and the risk factors,further explored the relationship between vitamin D and risk of preterm birth.MethodsThis study was based on Ma’anshan Birth Cohort Study(MABC).Pregnantwomen were recruited from May 2013 to September 2014 in prenatal clinics of Ma’anshan Maternal and Child Healthcare Hospital.Information of baseline characteristics(age,gestational age,education level,place of residence,average household income),pregnancy history(gravidity,parity,history of ill pregnancy),and smoking of pregnant women,vitamin D supplementation,pregnancy complications and fetal birth outcome were collected.Three trimester maternal serum were collected and serum 25(OH)D was measured using radioimmunoassay.One-way analysis of variance(ANOVA)and χ2 test was used to analysis the risk factors of prenatal vitamin D levels.Binary logistic regressions were conducted to determine the effect of three trimester maternal vitamin D level on risk of preterm birth.ResultsThe prevalence of vitamin D deficiency during three trimesters was 60.9%,22.5%and 59.6%,respectively.Compared to pregnant women which were sampled in summer,the prevalence of low vitamin D levels was greater in winter and spring(P<0.001).In addition,older age,primigravid,use of vitamin D supplementation were protective factors of vitamin D deficiency,pre-pregnancy overweight(pre-pregnancy BMI ≥ 24 kg/m2)is a risk factor for vitamin D deficiency.After controlling for maternal age,pre-pregnancy BMI,education level,place of residence,average household income,gravidity and season,the results suggested that vitamin D deficiency during second trimester is a risk factor for total PTB,spontaneous preterm birth(sPTB)and iatrogenic preterm birth(iPTB),OR values(95%CI)were 4.00(1.46~10.94)for total PTB,2.63(1.12~6.16)for sPTB,and 10.48(1.34~81.71)for iPTB.In addition,After adjustment for maternal age,pre-pregnancy BMI,education level,place of residence,average household income,gravidity and season,,the risk of total PTB significantly decreased as 25(OH)D increased to approximately23ng/ml and then plateaued(test of nonlinearity P=0.026).ConclusionOverall,our findings show that the prevalence of vitamin D deficiency is high among pregnant women in Ma’anshan,especially in the first trimester and third trimester.Vitamin D deficiency was related to maternal age,pre-pregnancy BMI,gravidity,vitamin D supplementation and season at sampling.We found that vitamin D deficiency during second trimesters could increase the risk of total PTB,sPTB and iPTB. |
