Pre-pregnancy body mass index and the risk of adverse outcome in type 1 diabetic pregnancies: a population-based cohort study

Martina Persson, Dharmintra Pasupathy, Ulf Hanson, Magnus Westgren, Mikael Norman
BMJ Open 2012, 2 (1): e000601

OBJECTIVE: To assess the risk of perinatal complications in overweight and obese women with and without type 1 diabetes (T1DM).

DESIGN: Prospective population-based cohort study.

SETTING: This study was based on data from the Swedish Medical Birth Registry from 1998 to 2007.

PARTICIPANTS: 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).

CONCLUSION: 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.

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