title: Critical periods of maternal weight gain: effect on twin birth weight.
abstract: OBJECTIVE
  Our purpose was to evaluate the association between maternal weight gain and twin birth weight.
  
  
  METHODS
  This historic cohort study was based on 646 live-born twin births of > or = 28 weeks from Baltimore, Maryland, Miami, Florida, and Ann Arbor, Michigan. The sum of twin-pair birth weight was modeled as a function of either net maternal weight at delivery or rates of maternal weight gain with use of multiple regression.
  
  
  RESULTS
  Birth weight was significantly associated with weight gain before 20 weeks in underweight women, before 20 weeks and after 28 weeks in overweight women, and during all three gestational periods in normal-weight women. Weight gain before 20 weeks had the largest effect on infants of underweight women, less of an effect on infants of normal-weight women, and half as much effect on infants of overweight women. Weight gain after 28 weeks significantly affected the infant birth weights of normal-weight and overweight women, but the effect was half as great among infants of the latter group.
  
  
  CONCLUSIONS
  These findings suggest that weight gain during critical periods of gestation significantly influences twin birth weight; these critical periods vary by maternal pregravid weight status.
authors.affiliation: Department of Obstetrics and Gynecology, University of Michigan Medical School, Ann Arbor 48109-0264, USA.
authors.forename: B
authors.initials: B
authors.lastname: Luke
authors.forename: B
authors.initials: B
authors.lastname: Gillespie
authors.forename: S J
authors.initials: SJ
authors.lastname: Min
authors.forename: M
authors.initials: M
authors.lastname: Avni
authors.forename: F R
authors.initials: FR
authors.lastname: Witter
authors.forename: M J
authors.initials: MJ
authors.lastname: O'Sullivan
mesh_terms: D000328:Adult; D001724:Birth Weight; D015331:Cohort Studies; D005260:Female; D006801:Humans; D007231:Infant, Newborn; D011247:Pregnancy; D014427:Twins; D015430:Weight Gain