Induction of labour and larger women: what are the consequences?

A few weeks ago, I spotted a paper titled “Influence of Maternal Obesity on Labor Induction: A Systematic Review and Meta‐Analysis”, which was published as an ‘early view’ paper in the Journal of Midwifery and Women’s Health. The contents struck me so much that I wrote about it as my ‘study of the month’ in my Birth Information Update, but I wanted to blog about this too, because the findings are important and yet are not getting as much attention as they deserve.

Ellis et al (2019), who are based in the USA, note that induction rates are highest in larger women. (This may or may not be true in every country, but we hear from a significant number of larger women from around the world (including the UK, the USA, Australia, New Zealand and several European countries) who are distressed about being told they ‘need’ to be induced because of their size, so it’s clearly of concern to many). There are complex reasons for the high induction rate in larger women, including the association of higher BMI with complications (although I am not aware of good evidence to show that induction of labour leads to better outcomes) and the fact that larger women tend, on average, to go into labour later than women of average weight, which means they have more chance of being told they need to be induced because they are ‘post-dates’. The fact that they may, on average, birth later also means that they have more appointments with health professionals during which induction may be recommended.

The authors of this paper were concerned because, despite the publication of studies claiming to demonstrate that induction reduces the caesarean section rate, “In all women, labor induction is associated with longer labor course, more dysfunctional labor patterns, increased use of interventions (epidural analgesia, invasive fetal monitoring, and instrumental or operative birth), and extended hospital stays.” (Ellis et al 2019). So they conducted a meta-analysis which considered ten cohort studies.

Ellis et al (2019) found that “caesarean birth was more common among women with obesity compared with women of normal weight following labor induction (Mantel‐Haenszel fixed‐effect odds ratio, 1.82; 95% CI, 1.55‐2.12; P < .001). Maternal obesity was associated with a longer time to birth, higher doses of prostaglandins, less frequent success of cervical ripening methods, and higher dose of synthetic oxytocin, as well as a longer time to birth after oxytocin use.”

Different people will take different things from these findings. Some will focus on the question of whether we need to change induction protocols for women who are larger, while others will be more concerned on letting larger women know that, whether or not they are at greater risk because of their size, this data confirm that they are at greater risk of ending up with intervention or operative birth than their average-sized friends if they opt for labour induction. What we don’t know – as I have discussed before – is whether this is because of issues directly caused by size or weight, or because larger women are treated differently by health care providers.

Ellis JA, Brown CM, Barger B et al (2019). Influence of Maternal Obesity on Labor Induction: A Systematic Review and Meta‐Analysis. Journal of Midwifery and Women’s Health. (Early view).
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