Outcomes for severely obese women starting labour care in an alongside midwifery unit in the UK: results from a national cohort study using the UK Midwifery Study System

Background Maternal obesity is associated with longer labour and an increased chance of a birth complication. In the UK severely obese women (with BMI>35kg/m2) are advised to plan birth in a consultant-led obstetric unit... [ view full abstract ]

Background

Maternal obesity is associated with longer labour and an increased chance of a birth complication. In the UK severely obese women (with BMI>35kg/m²) are advised to plan birth in a consultant-led obstetric unit (OU).  Analysis of Birthplace study data indicated that ‘otherwise healthy’ obese multiparous women had better outcomes than healthy nulliparous women of normal weight, but was based on women planning OU birth.  The UK Midwifery Study System (UKMidSS) Severe Obesity Study aimed to investigate maternal characteristics, labour care, progress and outcomes in severely obese women admitted to alongside midwifery units (AMUs) compared with other women admitted to AMUs.

Method

The UKMidSS Severe Obesity Study is a national cohort study of over 1200 women with booking BMI>35kg/m², starting labour care in AMUs in the UK between 1^st January and 31^st December 2016, and a matched comparison group of women with booking BMI≤35kg/m² admitted to the same AMUs. 

Data were collected using UKMidSS, a national research infrastructure for prospective data collection in all AMUs in the UK. Midwives reported ‘cases’ (women with BMI>35kg/m2) and ‘denominator data’ on admissions and births in response to monthly emails and completed online data collection forms for ‘cases’ and comparison women.

Our primary outcome was a composite measure of adverse maternal outcome.  Secondary outcomes included transfer, immersionin water, birth in water and ‘straightforward vaginal birth’.

We used log Poisson regression to calculate relative risks of each outcome in the severely obese cohort relative to the comparison group, adjusted for maternal characteristics.  All analyses were carried out separately by parity and overall, combining nulliparous and multiparous women. 

Results

Results presented will describe the characteristics of severely obese and comparison group women and will focus on outcomes relating to ‘normal birth’.

Conclusions and implications

The implications of the results for midwifery unit admission criteria and for midwives supporting women making decisions about place of birth will be considered.