Objective To determine which factors are associated with caesarean section (CS) in women with pre-gestational diabetes.

Design Population-based retrospective cohort study of 1428 singleton live born infants of women with type 1 or type 2 diabetes, using data from the Northern Diabetes in Pregnancy Survey for 1996-2008. Multiple logistic regression was used for the analyses and adjusted odds ratios (aOR) with 95% confidence intervals (CI) are presented.

Results The overall CS rate was 63.1%, with significant variation between primiparas (n=584) (63.5%), multiparas with previous CS (n=409) (89.7%) and without previous CS (n=433) (36.7%). In primiparas, duration of diabetes ≥10 years (aOR=1.88, 95% CI 1.24-2.85), maternal obesity (BMI ≥30kg/m2) (aOR=2.16, 95% CI 1.30-3.57), macrosomia (birthweight ≥4000g) (aOR=2.75, 95% CI 1.54-4.91) and preterm (<37 weeks) delivery (aOR=2.91, 95% CI 1.89-4.49) were independently associated with CS. Type of diabetes, existing microvascular complications (nephropathy, retinopathy and neuropathy) and periconception glycaemic control (glycosylated haemoglobin, HbA1c) were not associated with primary CS. In multiparas with a previous CS, 17.0% (n=69) underwent a trial of labour, of whom 60.6% delivered vaginally. Factors associated with CS in the current pregnancy were maternal age ≥35 years (aOR 2.59, 95% CI 1.02-6.57), previous neonatal death (aOR 0.13, 95% CI 0.03-0.62) and preterm delivery (aOR 3.62, 95% CI 1.51-8.71).

Conclusion The rate of both primary and repeat CS in women with diabetes is high. Of the predictors of CS in primiparas maternal obesity is the only pre-conception modifiable risk factor.