title: Prepregnancy body mass index, smoking during pregnancy, and infant birth weight.
abstract: OBJECTIVE
  Smoking during pregnancy is strongly associated with increased risk of small for gestational age (SGA) and low birth weight, whereas elevated prepregnancy body mass index (BMI) is associated with a decreased risk of SGA and greater birth weight. We investigated the combined effect of prenatal smoking and prepregnancy BMI on risk of SGA and on birth weight.
  
  
  METHODS
  A total of 34,928 singleton, term pregnancies in residents of New York City between 1995 and 2003 were evaluated in multivariable regression models of birth weight and risk of SGA.
  
  
  RESULTS
  Increasing prepregnancy BMI reduced the risk of SGA and increased birth weight. The effect of prenatal smoking on birth weight and SGA diminished in women as their prepregnancy BMI increased, such that prenatal smoking did not significantly impact the risk of SGA among women who were overweight or obese before pregnancy. Prenatal smoking decreased mean birth weight by 187 g (95% confidence interval [CI] -337, -37) among underweight women, by 129 g(95% CI -170, -87) among normal weight women, by 46 g (95% CI -113, +20) among overweight women, and by 75 g (95% CI -162, +11) among obese women.
  
  
  CONCLUSIONS
  This study suggests that the effect of smoking during pregnancy on SGA and birth weight is present in underweight and normal weight women but markedly reduced among obese and overweight women.
authors.affiliation: Department of Preventive Medicine, Mount Sinai School of Medicine, New York, NY. michele.lamerrill@mssm.edu
authors.forename: Michele
authors.initials: M
authors.lastname: La Merrill
authors.forename: Cheryl R
authors.initials: CR
authors.lastname: Stein
authors.forename: Philip
authors.initials: P
authors.lastname: Landrigan
authors.forename: Stephanie M
authors.initials: SM
authors.lastname: Engel
authors.forename: David A
authors.initials: DA
authors.lastname: Savitz
mesh_terms: D000328:Adult; D001719:Birth Certificates; D001724:Birth Weight / Q000187:drug effects*; D015992:Body Mass Index; D005260:Female; D006801:Humans; D009519:New York City / Q000453:epidemiology; D011247:Pregnancy; D012907:Smoking / Q000009:adverse effects* / Q000453:epidemiology; D055815:Young Adult