[A survival analysis approach to assess the association between maternal smoking during pregnancy and childhood obesity].
OBJECTIVE
It has been suggested that maternal smoking during pregnancy has an effect on childhood obesity. We previously clarified the association between maternal lifestyle habits practiced during pregnancy, including smoking, and childhood obesity and overweight at 9-10 years of age. In this study, we aimed to demonstrate this association through survival analysis.


METHODS
This study was based on an on-going community-based prospective cohort study initiated in the fetal stage called Project Koshu. The study population comprised of the participants of Project Koshu, who were children born in a rural Japanese area between 1991 and 1999 and their mothers. In this project, maternal smoking status during pregnancy was collected through a questionnaire and childhood anthropometric data were measured at annual medical check-ups from 3 years of age to 9-10 years of age. Using these data, we performed a survival analysis using the Kaplan-Meier method to compare the cumulative rate of childhood obesity and overweight between those with mothers who smoked during pregnancy and those who did not. Subsequently, we calculated the hazard ratio (HR) of the effect of maternal smoking during pregnancy on childhood obesity using the Cox proportional hazard model.


RESULTS
In the survival analysis of childhood obesity, we analyzed the data of 1428 children and their mothers (follow-up rate: 87.7%). Of these, 290 children (20.3%) became overweight and 92 children (6.4%) became obese between 3 years of age and 9-10 years of age. This shows that the cumulative rate of childhood obesity was significantly different between mothers with and without smoking habits (P < 0.001). Using the Cox proportional hazard model, we analyzed the data of 1204 children and their mothers (follow-up rate: 74.0%). Of these, 255 children (21.2%) became overweight and 76 children (6.3%) became obese between 3 years of age and 9-10 years of age. Maternal smoking during pregnancy was found to be associated with childhood obesity (HR, 2.0; 95% confidence interval (CI): 1.04-4.0). However, there was no significant association between maternal smoking during pregnancy and childhood overweight.


CONCLUSIONS
Our results suggest that the effect of fetal environmental factors on childhood obesity is more pronounced than that on childhood overweight. These results suggest that maternal smoking during pregnancy may be a significant factor in the association between fetal environment and post-delivery development.
Department of Health Sciences, Interdisciplinary Graduate School of Medicine and Engineering, University of Yamanashi, Chuo, Yamanashi, Japan.
Kohta
K
Suzuki
Miri
M
Sato
Daisuke
D
Ando
Naoki
N
Kondo
Zentaro
Z
Yamagata
D000328:Adult; D002648:Child; D002675:Child, Preschool; D015331:Cohort Studies; D005260:Female; D005500:Follow-Up Studies; D006801:Humans; D009765:Obesity / Q000453:epidemiology / Q000209:etiology*; D011247:Pregnancy; D011297:Prenatal Exposure Delayed Effects; D016016:Proportional Hazards Models; D011446:Prospective Studies; D012907:Smoking / Q000009:adverse effects*