Pregnancy-related Complications and Type 1 Diabetes
Researchers Look at Pre-pregnancy Body Mass Index and Adverse Outcomes
The research team published their findings in the February 2012 edition of the journal BMJ Open in the article “Pre-pregnancy body mass index and the risk of adverse outcome in type 1 diabetic pregnancies: a population-based cohort study.”
The study was based on data collected from the Swedish Medical Birth Registry. Data were from 1998 to 2007.
A total of 3,457 pregnant women with type 1 diabetes and 764,498 pregnant women who did not have diabetes were included in the study. Only women with data on BMI and who had singleton pregnancies were included.
The women were categorized into 3 groups according to their pre-pregnancy body mass index (BMI):
- normal weight (BMI: 18.5 to 24.9)
- overweight (BMI: 25 to 29.9)
- obese (BMI ≥30)
Researchers noted that type 1 diabetes was identified based on the ICD code O24.0.
The primary outcome was large for gestational age (LGA) infants (infants with a birth weight >90th percentile).
There were several secondary outcomes in the study: Caesarean section delivery, major malformations, neonatal overweight, perinatal mortality, preeclampsia, and pre-term delivery.
Logistic regression analysis was performed with the normal weight women who did not have diabetes (the reference category) and within the diabetic cohort with normal weight women with type 1 diabetes (the reference).
The researchers found that 35% of the pregnant women with type 1 diabetes were overweight, and 18% of the pregnant women with type 1 diabetes were obese. Additionally, they found that 26% of the pregnant women who did not have diabetes were overweight, and 11% of the pregnant women who did not have diabetes were obese.
It was noted that the greater the women’s BMI, the greater the incidence of adverse outcomes.
Odds ratios were adjusted for chronic hypertension, ethnicity, height, maternal age, parity, and smoking.
Compared with normal weight women who did not have diabetes, the adjusted odds ratio for obese women with type 1 diabetes for LGA was 13.26 (95% confidence interval [CI]: 11.27 to 15.59). Adjusted odds ratio for obese women with type 1 diabetes for major malformations was 4.11 (95% CI: 2.99 to 5.65), and for preeclampsia, it was 14.19 (95% CI: 11.50 to 17.50).
The research team concluded that type 1 diabetes was a significant effect modifier for 3 factors: the link between BMI and LGA, major malformations, and preeclampsia (p<0.001).
They also concluded that a high BMI pre-pregnancy is an important risk factor for adverse outcomes in pregnant women with type 1 diabetes. The combined impact of being overweight or obese and having type 1 diabetes represents the greatest risk for adverse outcomes. The researchers recommend women with type 1 diabetes strive toward a normal pre-pregnancy BMI.