Maternal risk exposure during pregnancy and infant birth weight

•The importance of the psychosocial qualities of a child’s immediate care and home environments in early life.•Unwanted pregnancy and tobacco use during pregnancy significantly lowered birth weight.•Exposure to multiple, relative to single risks, prenatally resulted in greater reductions in infant birth weight.

BackgroundBirth weight is an important determinant of an infant's immediate and future health.AimThis study examined associations between selected maternal psychosocial and environmental risk factors during pregnancy and subsequent infant birth weight, utilising data from the South African Birth to Twenty Plus (Bt20 +) birth cohort study.SubjectsExposure to nine maternal risks were assessed in 1228 women who completed an antenatal questionnaire and whose infants were delivered within a seven-week period.Outcome measuresThe outcome of interest was infant birth weight. Birth weight z-scores (BWZ) were calculated using the World Health Organization Child Growth Standards. Bivariate analyses and multiple regression models were used to identify significant risk factors.ResultsThe mean infant birth weight was 3139 g (SD 486 g), with a significant advantage in mean birth weight for male infants of 73 g (p = 0.008). Being unsure or not wanting the pregnancy was associated with a ~ 156 g reduction in infant birth weight (β = − 0.32; 95% CI − 0.51; − 0.14). Tobacco use during pregnancy was also negatively associated with BWZ (β = − 0.32; 95% CI − 0.59; − 0.05). Exposure to both significant risk factors (tobacco use and pregnancy wantedness) was associated with cumulative reductions in birth weight, particularly among boys.ConclusionsThis study reinforces the importance of risks related to maternal attitudes and behaviours during pregnancy, namely unwanted pregnancy and tobacco use, which significantly lowered birth weight. Both identified risks are amenable to public health policy and programme intervention.