title: The association of ambient outdoor temperature throughout pregnancy and offspring birthweight: findings from the Aberdeen Children of the 1950s cohort.
abstract: BACKGROUND
  We assessed the effect of mean ambient outdoor temperature during gestation on birthweight.
  
  
  OBJECTIVE
  To assess the effect of mean ambient outdoor temperature during gestation on birth weight.
  
  
  METHODS
  Birth cohort study with record linkage to climate databases.
  
  
  METHODS
  Aberdeen, Scotland.
  
  
  METHODS
  A total of 12,150 individuals born in Aberdeen, Scotland between 1950 and 1956.
  
  
  RESULTS
  Perinatal data from a cohort of 12,150 individuals born in Aberdeen, Scotland between 1950 and 1956 were linked to daily outdoor temperature data. Birthweight was seasonally patterned, with lowest birthweights among those born in the winter months (December-February) and highest birthweights among those born in the autumn months (September-November); P= 0.01 for joint sine-cosine functions. Mean ambient outdoor temperature during the first trimester of pregnancy was inversely associated with birthweight and mean ambient outdoor temperature during the third trimester of pregnancy was positively associated with birthweight. In fully adjusted (for sex, maternal age, birth year, birth order and social class) models a 1 degrees C increase in mean ambient outdoor temperature in the mid 10-day period of the first trimester was associated with a 5.4-g (95% confidence interval [CI] 2.9, 7.9 g) decrease in birthweight, whereas a 1 degrees C increase in the mid 10-day period of the third trimester was associated with a 1.3-g (95% CI 0.50, 2.1 g) increase in birthweight. Ambient outdoor temperature in the first trimester of pregnancy explained the seasonal patterning of birthweight.
  
  
  METHODS
  Birthweight.
  
  
  RESULTS
  Birthweight was seasonally patterned, with lowest birthweights among those born in the winter months (December-February) and highest birthweights among those born in the autumn months (September-November); P= 0.01 for joint sine-cosine functions. Mean ambient outdoor temperature during the first trimester of pregnancy was inversely associated with birthweight and mean ambient outdoor temperature during the third trimester of pregnancy was positively associated with birthweight. In fully adjusted (for sex, maternal age, birth year, birth order and social class) models a 1 degrees C increase in mean ambient outdoor temperature in the mid 10-day period of the first trimester was associated with a 5.4 g (95% confidence interval 2.9, 7.9 g) decrease in birthweight, whereas a 1 degrees C increase in the mid 10-day period of the third trimester was associated with a 1.3 g (95% confidence interval 0.50, 2.1 g) increase in birthweight. Ambient outdoor temperature in the first trimester of pregnancy explained the seasonal patterning of birthweight.
  
  
  CONCLUSIONS
  Higher ambient outdoor temperature in the first trimester of pregnancy and/or lower ambient outdoor temperature in the third trimester are associated with reduced offspring birthweight. With the increasing occurrence of temperature extremes, in particular, heat waves, these findings, if replicated in other studies, have important public health implications.
authors.affiliation: Department of Social Medicine, University of Bristol, Canyage Hall, Whiteladies Road, Bristol BS7 8PR, UK.
authors.forename: Debbie A
authors.initials: DA
authors.lastname: Lawlor
authors.forename: David A
authors.initials: DA
authors.lastname: Leon
authors.forename: George
authors.initials: G
authors.lastname: Davey Smith
mesh_terms: D000293:Adolescent; D000328:Adult; D001724:Birth Weight; D015331:Cohort Studies; D005260:Female; D005865:Gestational Age; D006801:Humans; D008297:Male; D008423:Maternal Age; D008875:Middle Aged; D011247:Pregnancy / Q000502:physiology*; D012044:Regression Analysis; D012606:Scotland / Q000453:epidemiology; D012621:Seasons; D012737:Sex Factors; D012923:Social Class; D013696:Temperature