The Optimal Postnatal Growth Trajectory For Small For Gestational Age Infants And Its Association With Maternal Pregnancy Vitamin D In The Third Trimester:a Birth Cohort Study

Objective To build multiclass growth trajectory for small for gestational age(SGA)infants based on latent class model,and select representative growth trajectory index to describe charactieras for catch-up growth.To identify the appropriate growth trajectory pattern by analysing predictive effect of growth trajectory on development behaviours,BMI and growth restriction among 0-18 months infants.To preliminarily explore the effect of maternal vitamin D level on growth trajectory for SGA infants.Methods Based on birth cohort study from Ma’anshan Municipal Hospital for Women and Children Health,the participants of the current study included 278 full-term single SGA infants and appreciate for gestational age(AGA)infants.Birth length,birth weight,head circumference index of infants aged 3 months,6 months,9 months and 12 months were measured,respectively.Birth length,birth weight and head circumference were transformed into height for age z-score(LAZ),weight for age z-score(WAZ),head circumference for age z-score(HCAZ)and weight for height z-score(WLZ)according to infants’ age.Latent class growth model(LCGM)and growth mixture model(GMM)were used to build growth trajectory models based on LAZ,WAZ,HCAZ,and WLZ separately.We attempted to select the optimal model and categories and screen the representative trajectory index.Behaviour development for SGA infants aged 6 months and 18 months were examined by Ages and Stages Questionnaires-Chinese,BMI and growth restriction for SGA infants aged 6 months,12 months and 18 months were evulated based on heatlh examination.AGA infants were defined as reference group,the association between different growth trajectories,growth and development were analyzed by logistic regression models.Radioimmunoassay was used to detect maternal(32-39 week)serum vitamin D levels of SGA infants.Information of participant mothers,including season of vitamin D test,vitamin D and Calcium supplements intaking,pre-pregnancy BMI,gestational weight gain,pregnancy complications,delivery mode,feeding pattern and hospitalization history in the first year were collected.We used logistic regression models to analyse the association of maternal vitamin D level and the growth trajectory among SGA infants.Results The indexes of LAZ,WAZ,HCAZ and WLZ were better in GMM than LCGM.The models comparison between LAZ,WAZ,HCAZ and WLZ showed that the 3 categories of WLZ was optimal.The probabilities of class Ⅰ,Ⅱ,and Ⅲ were 21.8%,64.7%,and 13.5%,respectively,and the probability distributions were reasonable.The class Ⅰ,Ⅱ,and Ⅲ could represent fast catch-up growth,moderate catch-up growth and delayed catch-up growth in SGA infants,respectively.The comparison of 3 class growth trajectory showed that 0-6 months was the critical period for catch-up growth,the catch-up speed were slow down or fall for most SGA infants more than 6 months.Inversely,a minority of SGA infants aged 0-6 months didn’t show catch-up growth till 3 months later and with slow speed.After controlled for confounding factors,the growth trajectory of class Ⅰ increased risks of subnormal for gross motion,fine motion,problem solving and personal-social region at age of 6 months,and the OR(95% CI)values were 2.18(1.17-4.04),2.24(1.17-4.28),2.31(1.23-4.36)and 2.36(1.28-4.34),respectively.Nevertheless,the growth returned to normal at age of 18 months.Moreover,the growth trajectory of class Ⅰ increased risk of high BMI at age of 6 months(OR,95%CI: 12.40,6.11-25.14).The growth trajectory of class Ⅲ increased risk of subnormal for gross motion(OR,95%CI: 3.32,1.63-6.77).At 6 months,the growth restriction rate of class Ⅲ was 16.1%,while the other group were both less than 3%.No significant difference of behavior development was found between catch-upⅡ group and AGA group in 6 month and 18 month age groups.The rate of high BMI in catch-upⅡ group was significant higher than that of AGA group.According to the results of the development assessment,the categories of Ⅰ,Ⅱ and Ⅲ for catch-up were named to 3 groups: fast catch-up growth,optimal catch-up growth and delayed catch-up growth.Compared with the optimal catch-up growth group,maternal vitamin D deficiency was a risk factor for fast catch up growth(OR,95%CI: 2.59,1.20-5.61)and delayed catch-up growth(OR,95%CI: 3.65,1.47-9.08),after controlled confounding factors including birth weight,season of vitamin D test,vitamin D and Calcium supplements intaking in pregnancy,infant gender,delivery mode,feeding pattern before 6 months,hospitalization history in the first year,maternal age,maternal education,pre-pregnancy BMI,gestational weight gain,gestational diabetes mellitus and hypertensive disorders in pregnancy.Conclusion The WLZ is the representative index of growth trajectory assessment for SGA infant and can be identified as 3 models: fast catch-up growth,optimal catch-up growth and delayed catch-up growth.Six months after birth is critical period for infants to catch up the optimal catch-up growth.Infants who are fast or delayed to catch up with growth will both increase the risk of early childhood developmental abnormalities and obesity/growth restriction.Maternal vitamin D deficiency is a risk factor for fast catch-up growth and delayed catch up growth for SGA infants.