Abstract
BackgroundIt is well known that maternal smoking during pregnancy and maternal pre-pregnancy overweight have opposite effects on the infants’ birth weight. We report on the association of the combination between both risk factors and the infants’ birth weight.MethodsWe studied 3241 infants born at term in the PIAMA birth cohort. Maternal smoking during pregnancy and pre-pregnancy height and weight were self-reported. Multivariable regression analysis was performed to assess the associations between infants of mothers who only smoked during pregnancy, who only had pre-pregnancy overweight and who had both risk factors simultaneously, on term birth weight and the risk of being SGA or LGA.ResultsOf 3241 infants, 421 infants (13%) were born to smoking, non-overweight mothers, 514 (15.8%) to non-smoking, overweight mothers, 129 (4%) to smoking and overweight mothers and 2177 (67%) to non-smoking, non-overweight mothers (reference group). Infants of mothers who smoked and also had pre-pregnancy overweight had similar term birth weight (− 26.6 g, 95%CI: − 113.0, 59.8), SGA risk (OR = 1.06, 95%CI: 0.56, 2.04), and LGA risk (OR = 1.09, 95%CI: 0.61, 1.96) as the reference group.ConclusionsOur findings suggested that the effects of maternal smoking during pregnancy and maternal pre-pregnancy overweight on infants’ birth weight cancel each other out. Therefore, birth weight may not be a good indicator of an infant’s health status in perinatal practice because it may mask potential health risks due to these maternal risk factors when both present together.
Highlights
It is well known that maternal smoking during pregnancy and maternal pre-pregnancy overweight have opposite effects on the infants’ birth weight
Infants of mothers who smoked during pregnancy have on average a lower birth weight and a greater risk of being small-for-gestational age (SGA) than those born to non-smoking mothers [1, 2, 4, 6]
In infants of mothers who smoked during pregnancy the mothers more often were younger than 25 years, compared to the reference group (9.8 and 10.2% versus 4.9% respectively)
Summary
It is well known that maternal smoking during pregnancy and maternal pre-pregnancy overweight have opposite effects on the infants’ birth weight. We report on the association of the combination between both risk factors and the infants’ birth weight. Maternal smoking during pregnancy and prepregnancy overweight are well-known examples of obstetric risk factors that have an impact on infants’ health [1,2,3,4,5]. Little is known about the combined effect of maternal smoking during pregnancy and maternal prepregnancy overweight on birth weight. The individual, opposite effects of maternal smoking and maternal overweight may either cancel each other out resulting in normal birth weight as was observed in a recent large population-based study [9], or the individual effect of one maternal risk factor may prevail over the other as was reported in a less recent, smaller study [10]. Birth weight is often used as an indicator of the infant’s health status which may not be valid for these common risk factors with opposite effects.
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