Sociodemographic, behavioral, obstetric, and healthcare factors associated with low weight at birth: a case-control study.

BACKGROUND: Understanding social determinants is crucial for implementing preventive strategies, especially for low birth weight (LBW)-a public health issue that severely increases the risk of morbimortality in children. OBJECTIVE: This study aimed to identify the factors associated with LBW among newborns, assisted by the Brazilian Unified Health System. DESIGN AND SETTING: It analyzed data from newborns and their mothers. The sample was selected by convenience from users of the public health system in Francisco Beltrão (Paraná, Brazil). METHODS: Cases (n = 26) were babies weighing ≤ 2,500 g and controls (n = 52) > 2,500 g. All babies were assessed and paired by sex and date of birth in a 1:2 proportion. Statistical power was computed a posteriori, revealing a power of 87% (α = 0.05). RESULTS: Strong and significant differences were found in the bivariate analysis, in which the number of current smokers or those who quit during pregnancy was higher among mothers of babies with LBW. Moreover, the gestational weeks were lower among these cases. Logistic regression models indicated that the gestational week (odds ratio [OR] = 0.17, 95% confidence interval [CI]:0.05-0.54) and fathers' educational level (high school or above; OR = 0.22, 95% CI:0.06-0.99) were related to lower chances of low birth weight. CONCLUSIONS: Our findings confirm previous investigations on LBW's multi-causality, showing that the gestational week could reduce up to 82% chances of a baby being born with ≤ 2,500 g. Its association with paternal education underlines the importance of comprehensive policies to protect newborns.