Pathways Linking Socio-economic Status To Small-for- Gestational Age (SGA) Infants Among Pregnant Women

Objective:We aimed to explore the direct and indirect effects of socio-economic status(SES)on small-for-gestational age(SGA)infants,which could provide scientific evidence for prevention and intervention of SGA infants.Methods:The study population which included a total of 8737 primiparae and their newborns was from the Health Baby Cohort(HBC)in Wuhan.Participants were recruited from pregnant women who took antenatal care and gave birth in the maternity care hospital of Wuhan between September 2012 and October 2014.We obtained the information of participants through questionnaires,health manual and medical records.The t-test,chi-square test and multivariate logistic regression analysis were performed to screen the risk factors of SGA.Pathway analysis was used to find out the mediators between SES and SGA.Results:(1)Among 8737 primiparae,927 pregnant women had babies with SGA and the prevalence of SGA was 10.61%.(2)Logistic regression analysis showed that the high SES was inversely associated with risk of SGA(OR,0.765;95%CI,0.665,0.881).After adjustment for potential confounders such as maternal age and pregnancy-induced hypertension(PIH),the OR for SGA with low SES was 0.853(95%CI,0.734,0.991).(3)The relationship between SES and SGA was completely mediated by pre-pregnancy body mass index(BMI),gestational weight gain(GWG),a multi-vitamin supplement during the first trimester of pregnancy,and PIH.The parameters of the goodness-of-fit test for this model were:RMSEA=0.012,CFI=0.968.In this model,there were four significant pathways between SES and SGA as following:(1)SES could reduce the risk of SGA via PIH(B=-0.030,P=0.020).Since PIH could increase the risk of SGA(B=0.166,P<0.001),high SES could lower the risk of SGA by avoiding PIH(B=-0.181,P<0.05).(2)SES could reduce the risk of SGA via a multi-vitamin supplement(B=-0.022,P=0.011).A multi-vitamin supplement could lead to a lower risk of SGA infants(B=-0.066,P<0.05).Therefore,high SES could reduce the risk of SGA via promoting to take a multi-vitamin supplement during early pregnancy(B=0.334,P<0.001).(3)SES could lower the risk of SGA via pre-pregnancy BMI?18.50kg/cm~2(B=-0.007,P=0.027).Pre-pregnancy BMI?18.50kg/cm~2 could decrease the risk of SGA infants(B=-0.274,P<0.001).Therefore,high SES could lower the risk of SGA infants through keeping pre-pregnancy BMI?18.50kg/cm~2(B=0.025,P<0.05)(4)SES could reduce the risk of SGA via pre-pregnancy BMI and GWG(B=-0.002,P=0.026).Pregnancy women with pre-pregnancy BMI?18.50kg/cm~2 were more likely to gain adequate gestational weight which was above Institute of Medicine(IOM)recommendations(B=0.254,P<0.001).And the GWG above IOM recommendations was a protector of SGA infants(B=-0.321,P<0.001).Therefore,high SES could reduce the risk of SGA via keeping pre-pregnancy BMI?18.50kg/cm~2 firstly(B=0.033,P<0.05),and then gain adequate gestational weight.Conclusions:The relationship between SES and SGA was mediated by the four pathways of PIH,taking a multi-vitamin supplement during early pregnancy,keeping normal pre-pregnancy BMI and GWG above IOM recommendations.