Shoulder Dystocia

What?

Shoulder dystocia is when the baby’s head is born but the shoulders become stuck. It is quite rare, occurring in less than half a percent (1 in 200) births in the UK.

It’s serious, because although the baby’s head is outside its mother’s body, it cannot breathe while its chest is squashed inside the mother’s pelvis. At the same time the baby’s own body is squashing the umbilical cord, restricting the supply of oxygen. So it is important that the baby’s shoulders are released and the baby born as soon as possible.

Being at higher risk of shoulder dystocia is one of the many scare stories we hear as bigger people. You may hear that you have ‘triple’ or ‘quadruple’ the risk, which sounds extreme and very alarming! This is because an American study of Swedish data reported shoulder dystocia in 0.1% (1 in 1000) births in ‘normal’ weight women, 0.3% (3 in 1000) births of women with BMI 29-35, and 0.4% (4 in 1000) of women with BMI 35-40.

It is a popular reason to restrict bigger women and birthing people’s choices of how and where we birth.

Why?

Because the consequences for the mum and baby aren’t great. The mum has a possibility of post partum haemorrhage, 3rd and even 4th degree tears. More severe are the potential consequences for the baby; broken bones, limb paralysis, brain damage, and even death. (It’s worth saying right now that these outcomes are very rare; most incidences of shoulder dystocia are resolved quickly and without issue).

But any mention of a 4x risk of a baby dying is usually enough to send any prospective parent scuttling into whatever corner is recommended. But is this fair? Are medical professionals ‘pulling the dead baby card‘ – scaring us into taking the course of action which suits them rather than listening to us as their patient?

How?

No-one really knows how or why shoulder dystocia happens. It’s a risk with any vaginal delivery in women of any size. That’s not to say I’m advocating for elective caesareans, there are plenty of risks associated with surgical delivery; including some of the same serious consequences seen when shoulder dystocia goes badly wrong. A great many occur in women with no risk factors whatsoever. There has been some evidence to show it’s marginally less likely if you’re taller, but there are no guarantees.

In fact, the Royal College of Obstetricians and Gynaecologists’ guideline explains that statistical prediction models are only able to successfully predict 16% of cases;

“Risk assessments for the prediction of shoulder dystocia are insufficiently predictive to allow prevention of the large majority of cases.”
“The use of shoulder dystocia prediction models cannot therefore be recommended.”

So, hang on a second. The RCOG says there’s no way to reliably predict shoulder dystocia. Yet we’re often pressured not to birth at home, or in a midwife led unit (or in water in some hospitals) because its more likely?

I grant you that a 4 in 1000 risk is 4x the risk someone with a lower BMI can expect, but to restrict my birth choices on the basis of something 99.6% not likely to happen? Anyone else see a problem with that?

Who?

Factors associated with shoulder dystocia:

previous shoulder dystocia (this seems to be a strong indicator, with between a 1% and 25% chance of it happening again)
large (macrosomic) baby i.e. >4.5kg
diabetes in the mother (gestational diabetes)
maternal BMI >30
induction of labour
slow progress of labour
assisted delivery

Now I can see some co-morbidity here, which could be skewing the figures. We know that higher BMI pregnancies are more likely to be induced, induction is more likely to lead to a labour which is deemed ‘slow to progress’, which is more likely to lead to assisted delivery, all of which are associated with a higher rate of shoulder dystocia. So did the induction somehow lead to the shoulder dystocia, or did the shoulder dystocia cause the prolonged labour? Or is there merely a correlation between dystocia and the above factors?

We also know that a bigger mum is more likely to be diabetic. A diabetic mum is more likely have a large baby. A large baby is more likely to experience shoulder dystocia. But what about non-diabetic big mums? Or diabetic mums not having large babies? Is it BMI that’s relevant, being diabetic, or a large baby? Or all three? Or a combination?

Two studies noted that babies born to diabetic mothers were more likely to have shoulder dystocia than babies weighing the same born to non-diabetic mothers, so that would imply that diabetes is more important than birth weight, but the researchers didn’t make any distinctions on the basis of maternal weight, so we still can’t see where BMI fits into the picture.

Recent but as-yet-unpublished data (2019)

One group of researchers, who as of January 2022 don’t yet appear to have published, but have presented their findings at a conference, did find an association purely between BMI and shoulder dystocia, irrespective of diabetes status. They even looked at the statistics for people with pre-existing diabetes and gestational diabetes separately! But without a published, peer-reviewed article to assess, it’s hard to know how much stock to put in this. Apologies for the dreadful image quality, this is directly from the source!

Confounding co-morbidities again!

The trouble with people is that we’re complex. We don’t belong in just one discrete category. It’s helpful if researchers are beginning to pull apart the data in this way – it’s something I’ve been pushing for for years! But it still doesn’t give the whole picture.

Someone who is large, diagnosed with gestational diabetes, whose labour is induced and deemed ‘slow to progress’, who then has an assisted delivery of a large baby with shoulder dystocia pops a mark in the box for all of those factors.

We know from other studies that the threshold to intervene in labour in higher BMI cases is lower. Is the intervention itself a causal factor, a correlation, or is some other factor influencing both? We don’t know, without specific research to look into it.

We do know that if we don’t exclude the data where more than one factor may have influenced the outcome, we risk confusing the issues. This potentially inflicts unnecessary restrictions and/or interventions on people whose shared characteristics may be unconnected with the problem.

When?

Many bigger mums are scared into (or out of) treatment when they’re told the risk is greater for larger babies, and are then told their baby is measuring ‘on the big side’. But the truth is that most large babies are born without issue, and in fact, almost half (48%) of all shoulder dystocia cases were of babies weighing less than 4 kg. So maybe the big baby thing is a red herring?

We also need to remember that studies which draw a link between shoulder dystocia and fetal weight tend to do so based on actual birth weight. The obvious huge flaw with this is that this information is only available in hindsight! It is only estimated birth weight which is available when we’re making decisions, and that is notoriously innaccurate.

The RCOG’s own guidance on shoulder dystocia says estimated birth weight should never be the sole reason for any treatment decision.

Estimation of fetal weight [EFW] is unreliable and the large majority of infants over 4.5kg do not experience shoulder dystocia. In the USA, a decision-analysis model estimated that in non-diabetic women with an EFW of >4kg, an additional 2345 caesarean deliveries would be required, at a cost of US$4.9 million, to prevent one permanent injury from shoulder dystocia.
RCOG – Green-top Guideline No. 42 – Shoulder Dystocia

What if?

Midwives and obstetric professionals have extensive training in spotting and dealing with shoulder dystocia. If diagnosed, speed is paramount; it is rare for serious injury or death to occur if resolved in under 5 minutes.

The first line of treatment is usually something called the McRoberts’ manoeuvre. This is where the mother is instructed to resist the urge to push, to lie flat on her back, and to bring her knees up as far as possible to her shoulders so her thighs are resting on her abdomen (with help, if necessary!). This opens space in the pelvis allowing the shoulders more room and is apparently successful in resolving dystocias in up to 90% of cases.

Trials of putting women into the McRoberts’ position before delivery, with the aim of preventing shoulder dystocia, have not shown any level of success, so luckily we’re not all urged to deliver like that as a precaution. Thank goodness!

If the McRoberts’ manouevre is unsuccessful then there are more invasive actions to try. These involve the midwife or obstetrician trying to manually rotate the baby’s shoulders and/or ease an arm out to facilitate delivery, but these carry greater risk of harm. With the exception of a caesarean delivery, all the procedures to resolve shoulder dystocia can be done by a midwife at home, and all midwives receive extensive training on these procedures.

And finally…

So as usual, as bigger mums we’re being told there’s 3x times the risk / 4x times the risk of something bad happening, but not the information that the risk actually 3 or 4 in 1000.

We’re also rarely told that in 90% of cases the issue is resolved simply by changing position.

Obviously the consequences for the baby can be severe, but permanent injury occurs in just 2 in 10,000 births. Personally, I think this is the information we need when making an informed decision!

Perhaps it is telling that shoulder dystocia accounts for a significant number of medical lawsuits in the UK. It’s the 3rd most likely reason for litigation. Could this be the real reason Healthcare Professionals and hospital trusts attempt to restrict our choices?