title: Maternal Leisure Time Physical Activity and Infant Birth Size.
abstract: BACKGROUND
  Associations of maternal leisure time physical activity with birth size are inconsistent. Roles of infant sex and maternal prepregnancy body mass index (BMI) in these associations have not been studied.
  
  
  METHODS
  Participants (N = 3,310) in the Omega study, a cohort in Washington State (1996-2008), reported leisure time physical activity duration and energy expenditure in the year prepregnancy and in early pregnancy (mean 15 weeks gestation). Regression models estimated mean differences in infant head circumference, birthweight, and ponderal index (birthweight/length) across quartiles of pre- or early-pregnancy leisure time physical activity. We assessed effect modification by infant sex or prepregnancy overweight/obese status (BMI ≥ 25 kg/m).
  
  
  RESULTS
  We observed positive associations between prepregnancy leisure time physical activity and head circumference overall and among male infants. Among males, each quartile increase in prepregnancy physical activity duration was associated with 0.14 cm (95% confidence interval = 0.046, 0.24; trend P = 0.004) greater head circumference. We did not observe associations between leisure time physical activity and birthweight or ponderal index overall. Each quartile increase in pre- or early-pregnancy physical activity duration was associated with 17-23 g lower birthweight among female infants and among women with normal prepregnancy BMI.
  
  
  CONCLUSIONS
  We observed positive associations between prepregnancy leisure time physical activity and head circumference among male infants, and inverse associations of pre- and early-pregnancy physical activity with birthweight among female infants and women with normal prepregnancy BMI. Future studies should confirm results and elucidate mechanisms of observed associations.
authors.affiliation: From the aDepartment of Epidemiology, University of Washington School of Public Health, Seattle, WA; bCenter for Perinatal Studies, Swedish Medical Center, Seattle, WA; and cDepartment of Epidemiology, Harvard T.H. Chan School of Public Health, Boston, MA.
authors.forename: Sylvia E
authors.initials: SE
authors.lastname: Badon
authors.forename: Pandora L
authors.initials: PL
authors.lastname: Wander
authors.forename: Chunfang
authors.initials: C
authors.lastname: Qiu
authors.forename: Raymond S
authors.initials: RS
authors.lastname: Miller
authors.forename: Michelle A
authors.initials: MA
authors.lastname: Williams
authors.forename: Daniel A
authors.initials: DA
authors.lastname: Enquobahrie
mesh_terms: D000293:Adolescent; D000328:Adult; D001724:Birth Weight; D015992:Body Mass Index; D005260:Female; D006257:Head / Q000033:anatomy & histology*; D006801:Humans; D007231:Infant, Newborn; D007899:Leisure Activities; D008297:Male; D009043:Motor Activity; D009765:Obesity; D050177:Overweight; D011247:Pregnancy; D011248:Pregnancy Complications; D011446:Prospective Studies; D012737:Sex Factors; D055815:Young Adult