title: Association between Maternal Smoking during Pregnancy and Low Birthweight: Effects by Maternal Age.
abstract: BACKGROUND
  Maternal smoking during pregnancy has been consistently related to low birthweight. However, older mothers, who are already at risk of giving birth to low birthweight infants, might be even more susceptible to the effects of maternal smoking. Therefore, this study aimed to examine the modified association between maternal smoking and low birthweight by maternal age.
  
  
  METHODS
  Data were obtained from a questionnaire survey of all mothers of children born between 2004 and 2010 in Okinawa, Japan who underwent medical check-ups at age 3 months. Variables assessed were maternal smoking during pregnancy, maternal age, gestational age, parity, birth year, and complications during pregnancy. Stratified analyses were performed using a logistic regression model.
  
  
  RESULTS
  In total, 92641 participants provided complete information on all variables. Over the 7 years studied, the proportion of mothers smoking during pregnancy decreased from 10.6% to 5.0%, while the prevalence of low birthweight did not change remarkably (around 10%). Maternal smoking was significantly associated with low birthweight in all age groups. The strength of the association increased with maternal age, both in crude and adjusted models.
  
  
  CONCLUSIONS
  Consistent with previous studies conducted in Western countries, this study demonstrates that maternal age has a modifying effect on the association between maternal smoking and birthweight. This finding suggests that specific education and health care programs for older smoking mothers are important to improve their foetal growth.
authors.affiliation: Department of Social Medicine and Health Education, School of Public Health, Peking University Health Science Center, Beijing, China.|Department of Health Sciences, Interdisciplinary Graduate School of Medicine and Engineering, University of Yamanashi, Chuo, Yamanashi, Japan.
authors.forename: Wei
authors.initials: W
authors.lastname: Zheng
authors.affiliation: Department of Health Sciences, Interdisciplinary Graduate School of Medicine and Engineering, University of Yamanashi, Chuo, Yamanashi, Japan.
authors.forename: Kohta
authors.initials: K
authors.lastname: Suzuki
authors.affiliation: Department of Social Medicine, Faculty of Medicine, Toho University, 5-21-16 Ohmorinisi, Ohta Ward, Tokyo, Japan.
authors.forename: Taichiro
authors.initials: T
authors.lastname: Tanaka
authors.affiliation: Department of Pediatrics, Okinawa Prefectural Chubu Hospital, Okinawa, Okinawa, Japan.
authors.forename: Moriyasu
authors.initials: M
authors.lastname: Kohama
authors.affiliation: Department of Health Sciences, Interdisciplinary Graduate School of Medicine and Engineering, University of Yamanashi, Chuo, Yamanashi, Japan.
authors.forename: Zentaro
authors.initials: Z
authors.lastname: Yamagata
mesh_terms: D000328:Adult; D005260:Female; D005865:Gestational Age; D006801:Humans; D007230:Infant, Low Birth Weight / Q000502:physiology*; D007231:Infant, Newborn; D016015:Logistic Models; D008423:Maternal Age; D009035:Mothers / Q000706:statistics & numerical data; D010298:Parity; D011247:Pregnancy; D012907:Smoking / Q000009:adverse effects*; D055815:Young Adult