To Örebro University

We compared birth trauma rates in pregnancies among women with and without type 1 diabetes (DM1) and tested the relationship with maternal body mass index (BMI) and large for gestational age (LGA) as a risk factor. This is a population-based cohort study 1998-2012 using the Swedish Medical Birth Registry (MBR) which includes 99% of Swedish pregnancies. All pregnancies up until gestational week 41 were included. We excluded mothers with other types of diabetes, duplex pregnancies and all pregnancies ending with a caesarean section (51.1% and 16.5% in women with and without DM1 respectively). The incidence of birth trauma was adjusted for BMI, maternal age, parity, Nordic or non-Nordic origin, smoking, chronic hypertensive disease, LGA and the baby ́s sex using logistic regression. This left 2,758 and 783,412 births with complete data among DM1 and control mothers respectively. The mean BMI, maternal age and gestational age at birth in full weeks was 25.6 (SD 4.5), 30.0 (SD 5.1) and 37.9 (SD 1.9) respectively among women with DM1 and 24.2 (SD 4.3), 29.7 (SD 5.1) and 38.9 (SD 1.5) respectively among controls. Preliminary results show that birth trauma rates did not vary significantly with increasing BMI compared with the reference BMI (18.50-24.9 kg/m2) among women with DM1 (odds ratios (OR) with increasing BMI (<18.49, 25.0-29.9, 30.0-34.9, >35.0 kg/m2) were 1.9 (95%CI 0.2-15.7), 1.0 (95%CI 0.7-1.5), 0.5 (95%CI 0.2-1.0), 1.1 (95%CI 0.5-2.4) respectively). Conversely, among controls, the OR for birth trauma increasedwith increasing BMI: 0.7 (95%CI 0.6-0.9), 1.4 (95%CI 1.3-1.5), 1.8 (95%CI 1.6-2.0), and 2.2 (95%CI 1.9-2.4) respectively. However, birth trauma was 3.9 (95%CI 2.7-5.7) and 7.0 (95%CI 6.5-7.5) fold more common after adjustment with LGA among women with andwithout DM1 respectively. We conclude that birth trauma rates are associated with LGA with comparatively greater impact among women without, than with, DM1. LGA is clearly an important outcome in its own right and a predictor of birth trauma. We hypothesise that the reduced risk of birth trauma from LGA among women with DM1 is due to increased monitoring with multiple ultrasounds to determine the fetal growth rate, along with earlier planned delivery (including earlier induction with vaginal delivery ata lower birthweight or caesarean section). While more research is needed to find better ways to reduce LGA in DM1, many of the obese control women would have undiagnosed/untreated GDM due to the Swedish criteria at the time (2 hours >=9.0mmol/l). Besidestreating lower levels of hyperglycaemia during pregnancy, the frequency of growth monitoring in obese mothers to reduce their babies’ risk of birth trauma due to LGA, needs to be evaluated. Life course cost effectiveness analyses would be useful.