Effect of maternal smoking during pregnancy on gestational weight gain and birthweight: A stratified analysis by pregestational weight status.

INTRODUCTION: In Japan, low birthweight (LBW) of infants is a major public health concern. Gestational weight gain (GWG) may be associated with LBW of infants. On the other hand, maternal smoking during pregnancy is a well-known factor associated with infant birthweight. Thus, this study aimed to examine the effect of maternal smoking during pregnancy on GWG and birthweight stratified by pregestational weight status.

METHODS: A retrospective cohort study was designed, which included three hospitals of Yamanashi Prefecture, Japan. The study included babies born between 2013 and 2014 from mothers having singleton pregnancies. The outcomes analyzed were GWG (difference between maternal weight measured at prenatal check-up just before delivery and pregestational weight based on information from clinical records) and birthweight of infants stratified by pregestational maternal body mass index (BMI).

RESULTS: This study included 1150 singleton babies and their mothers. After excluding individuals with incomplete data, the final number of analyzed participants was 1078. The mean maternal age at delivery was 31.3 ± 5.1 years. The mean pregestational BMI was 21.3 ± 3.4 kg/m2 . The mean GWG was 10.0 ± 4.1 kg. After adjusting for confounding factors, maternal smoking during pregnancy was positively associated with GWG in all categories (underweight: p<0.0001; normal weight: p<0.0001; overweight: p=0.01). Maternal smoking during pregnancy was also significantly associated with lower birthweight in underweight and normal-weight mothers (underweight: p=0.04, normal-weight: p=0.03).

CONCLUSIONS: Maternal smoking status is significantly associated with higher GWG and lower birthweight. Based on the Developmental Origins of Health and Disease (DOHaD) hypothesis, the growth of infants born from smoking mothers needs close observation.