Abstract
ABSTRACTOBJECTIVETo analyze the effects of maternal pre-pregnancy body mass index and weight gain during pregnancy on the baby's birth weight.METHODSWe conducted a cross-sectional study with 5,024 mothers and their newborns using a Brazilian birth cohort study. In the proposed model, estimated by structural equation modeling, we tested socioeconomic status, age, marital status, pre-pregnancy body mass index, smoking habit and alcohol consumption during pregnancy, hypertension and gestational diabetes, gestational weight gain, and type of delivery as determinants of the baby's birth weight.RESULTSFor a gain of 4 kg/m2 (1 Standard Deviation [SD]) in pre-pregnancy body mass index, there was a 0.126 SD increase in birth weight, corresponding to 68 grams (p < 0.001). A 6 kg increase (1 SD) in gestational weight gain represented a 0.280 SD increase in newborn weight, correponding to 151.2 grams (p < 0.001). The positive effect of pre-pregnancy body mass index on birth weight was direct (standardized coefficient [SC] = 0.202; p < 0.001), but the negative indirect effect was small (SC = -0.076, p < 0.001) and partially mediated by the lower weight gain during pregnancy (SC = -0.070, p < 0.001). The positive effect of weight gain during pregnany on birth weight was predominantly direct (SC = 0.269, p < 0.001), with a small indirect effect of cesarean delivery (SC = 0.011; p < 0.001). Women with a higher pre-pregnancy body mass index gained less weight during pregnancy (p < 0.001).CONCLUSIONSThe effect of gestational weight gain on the increase in birth weight was greater than that of pre-pregnancy body mass index.
Highlights
Birth weight is an indicator of perinatal risk and has been used in epidemiological studies as a representation of fetal nutritional exposure
We considered the following adjustment indices to determine whether the model showed goof fit: a) p-value (p) higher than 0.05 for the chi-square test[12], b) p < 0.05 and an upper limit of the 90% confidence interval of less than 0.08 for the root mean square error of approximation (RMSEA)[25], c) values higher than 0.95 for the comparative fit index and the Tucker-Lewis Index (CFI/TLI)[25], and d) values lower than one for the weighted root mean square residual (WRMR)[25]
In the analyses of the standardized estimates for the construction of the latent variable, we considered a factor load of more than 0.5 with p < 0.05 to indicate that the correlation between the variable observed and the construct was of moderately high magnitude[12]
Summary
Birth weight is an indicator of perinatal risk and has been used in epidemiological studies as a representation of fetal nutritional exposure. Birth weight reflects the conditions of pregnancy and influences the quality of life, the growth, and the development of the child, as well as childhood morbidity and mortality[22]. Important among the factors that influence birth weight are the pre-pregnancy and gestational inadequacies of the maternal nutritional status[20,27]. Pre-pregnancy overweight and obesity have been associated with gestational hypertension and diabetes, preterm birth, cesarean delivery, and low or high birth weight[22,27]. A low pre-pregnancy body mass index (BMI) has been associated with low birth weight and preterm birth[22]
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