title: Pre-pregnancy body mass index and the risk of adverse outcome in type 1 diabetic pregnancies: a population-based cohort study.
abstract: OBJECTIVE
  To assess the risk of perinatal complications in overweight and obese women with and without type 1 diabetes (T1DM).
  
  
  METHODS
  Prospective population-based cohort study.
  
  
  METHODS
  This study was based on data from the Swedish Medical Birth Registry from 1998 to 2007.
  
  
  METHODS
  3457 T1DM and 764 498 non-diabetic pregnancies were included. T1DM was identified based on ICD code O24.0. Mothers were categorised according to pre-pregnancy body mass index (BMI: weight in kilograms per height in square metres) as normal weight (BMI 18.5-24.9), overweight (BMI 25-29.9) or obese (BMI ≥30). Only women with singleton pregnancies and with data on BMI were included.  PRIMARY/SECONDARY OUTCOMES:  The primary outcome was large for gestational age (LGA: birth weight >90th percentile) infants. Secondary outcomes were major malformations, pre-eclampsia (PE), preterm delivery, perinatal mortality, delivery by Caesarean section and neonatal overweight. Logistic regression analysis was performed with normal weight non-diabetic women as the reference category and also within the diabetic cohort with normal weight type 1 diabetic women as the reference. The ORs were adjusted for ethnicity, maternal age, height, parity, smoking and chronic hypertension.
  
  
  RESULTS
  35% of women with T1DM were overweight and 18% were obese, as compared with 26% and 11%, respectively, in non-diabetic pregnancies. The incidences of adverse outcome increased with greater BMI category. As compared with non-diabetic normal weight women, the adjusted OR for obese T1DM for LGA was 13.26 (95% CI 11.27 to 15.59), major malformations 4.11 (95% CI 2.99 to 5.65) and PE 14.19 (95% CI 11.50 to 17.50). T1DM was a significant effect modifier of the association between BMI and LGA, major malformations and PE (p<0.001).
  
  
  CONCLUSIONS
  High pre-pregnancy BMI is an important risk factor for adverse outcome in type 1 diabetic pregnancies. The combined effect of both T1DM and overweight or obesity constitutes the greatest risk. It seems prudent to strive towards normal pre-pregnancy BMI in women with T1DM.
authors.affiliation: Department of Clinical Science, Intervention and Technology, Karolinska Institute, Stockholm, Sweden.
authors.forename: Martina
authors.initials: M
authors.lastname: Persson
authors.forename: Dharmintra
authors.initials: D
authors.lastname: Pasupathy
authors.forename: Ulf
authors.initials: U
authors.lastname: Hanson
authors.forename: Magnus
authors.initials: M
authors.lastname: Westgren
authors.forename: Mikael
authors.initials: M
authors.lastname: Norman