I have become increasingly concerned about guidelines and practices relating to induction of labour for larger women.
Women with a higher BMI have long been told that they need their labour induced because of their size (Cedergren et al 2004), despite a lack of evidence showing that this is beneficial (Wickham 2023).
I’m going to offer an overview of some of the key issues in this blog post. Please see either In Your Own Time or my Plus Size Pregnancy book for a readable discussion of the evidence on this and many other areas.
No trial evidence
When it comes to suggesting induction of labour because a woman has a higher BMI:
“There are no randomised controlled trials that have looked at outcomes relating to larger women and induction of labour. So we don’t have any robust evidence to tell us whether or not induction is beneficial for larger women or their babies.” (Wickham 2021).
“We do have some data from retrospective studies, which look back at women’s medical records to see what happened in different groups of women, but the results are very mixed and not very reliable.” (Wickham 2021).
So the first thing to know is that there is no evidence to support this recommendation.
A lack of evidence
In fact, the evidence in many areas relating to higher BMI is complicated and not very reliable.
This is partly because we know that larger women are more likely to be told they need intervention of all kinds, including induction and caesarean.
We know that their care and outcomes are affected by the attitudes (including weight bias, or fatphobia) of their caregivers.
And their progress in labour may be impeded by biased guidelines that restrict what they are able to do.
For instance, women with a higher BMI may be told they need to be monitored, which can mean they are less able to be active in labour, and they may be told that they aren’t able to use water during labour and birth.
The impact of culture
Many of the interventions and restrictions that are in place for women with a higher BMI are not evidence-based, but they can lower a woman’s chance of having a physiological birth.
This means that we have to take the outcomes of studies with a pinch of salt. Because we cannot know whether the higher rates of caesarean seen in some studies of women with a higher BMI have anything to do with the size or shape of the women.
My analysis of the research tells me that, in most cases, BMI may not be the issue. The outcomes seen in women with a higher BMI are likely more related to the restrictive guidelines imposed from within maternity services, and the weight bias that pervades modern culture.
Ellis et al (2019) are based in the USA, and they had noted that induction rates are highest in larger women.
They were concerned because they were also aware of the evidence They knew that, 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 carried out a systematic review and meta‐analysis of this area.
What did they find?
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.”
And what does that mean?
In a nutshell, this mean that women with a higher BMI may be even more likely to experience negative consequences after induction than women who have an average BMI.
Some people have questioned whether we need to change induction protocols for plus size women as a result of these findings.
But I think there is a more important and immediate issue. We need to ensure that women with a higher BMI know 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.
There is another reason that this is an important thing to share.
BMI, birth time and intervention
We also know that, on average, women with a higher BMI are more likely to get an inaccurate due date and may birth later than women with an average BMI.
(We don’t know why this is, but please see my Plus Size Pregnancy book for more discussion.)
This means that women with a higher BMI have more chance of being told they need to be induced because they are ‘post-dates’.
They may also end up having more appointments with health professionals during which induction may be recommended. That’s both because they are (on average) pregnant for longer, and because of the way that BMI is seen as a risk factor.
These are just some of the reasons that women with a higher BMI are more likely to end up with intervention. And I hope this helps explain why I say that it may not be because of anything to do with their actual body. Instead, the higher intervention rates stem (at least partly) from the way that larger women are treated in systems of health care.
If this affects you, I’ve written two books that will help you understand the issues and the evidence so you can make the decisions that are right for you.
Cedergren MI (2004). Maternal morbid obesity and the risk of adverse pregnancy outcome. O&G 103(2): 219-24.
Ellis JA, Brown CM, Barger B et al (2019). Influence of Maternal Obesity on Labor Induction: A Systematic Review and Meta‐Analysis. JMWH 64(1): 55-67.
Wickham S (2021). In Your Own Time: how western medicine controls the start of labour and why this needs to stop. Avebury: Birthmoon Creations.
Wickham S (2023). Plus Size Pregnancy: what the evidence really says about higher BMI and birth. Avebury: Birthmoon Creations.
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