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, the baby cannot breathe as its chest is being squashed by the mother’s pelvis. At the same time the baby’s own body is squashing the umbilical cord, restricting the supply of oxygen, and 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 thrown at bigger mums, because an American study of Swedish data found that while it was found in 0.1% (1 in 1000) births in ‘normal’ weight women, it occurred in 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 given for restricting the choices in how and where we give birth as bigger women.

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.

Any mention of a four times greater risk of their baby dying is usually enough to send a prospective mother scuttling into whatever corner has been recommended to her. But is this fair? Are medical professionals ‘pulling the dead baby card‘ – scaring mums into taking the course of action which suits them rather than their patient?

How?

No-one really knows how or why shoulder dystocia happens, it is always a risk with any vaginal delivery in women of any size (I am not advocating for elective caesareans here, there are plenty of risks associated with surgical delivery too). A great many occur in women with no risk factors whatsoever.

In fact, the Royal College of Obstetricians and Gynaecologists’ guideline, explains that although there are factors associated with shoulder dystocia, they cannot reliably indicate its likely occurrence. Thus far, statistical prediction models are only able to successfully predict 16% of cases! So the RCOG goes on to say;

“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 is saying that dystocia can’t be predicted, yet it’s given as a reason for not birthing at home, or in a midwife led unit (or in some hospitals birth in water) because of the possibility of it happening being more likely?

I grant you that a 4 in 1000 risk is 4x the risk a ‘normal’ weight mum 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 which are reported to be associated with shoulder dystocia are:

  • 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 high BMI mums 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 being big that is associated, being diabetic, or carrying 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.

The trouble with people is that we’re complex. We don’t belong in just one discrete category. A large diabetic mum, whose labour is induced and is slow to progress, and who has an assisted delivery of a large baby with shoulder dystocia pops a mark in the box for all of those factors.

If, when looking at the statistics, we don’t exclude the data of cases where more than one factor may have influenced the outcome, we risk confusing the issues. What’s worse, we then risk inflicting unnecessary restrictions and or treatments on other mothers who only share one or two characteristics with the person whose experience we’re trying to avoid, and for whom the shared characteristics may actually have been unconnected with the problem.

When?

Many bigger mums are scared into (or out of) treatment when they’re told of the risk being 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, which is obviously measured afterwards, rather than estimated birth weight, which is the only information available at the time of making decisions! Estimated birth weight from scan measurements is notoriously innaccurate, and should never be the sole reason for any treatment decision.

What if?

All midwives and obstetric professionals are trained to spot and deal with shoulder dystocia. If it is diagnosed, it is important that it is resolved within 5 minutes, as there are few documented cases of serious injury or death occurring within this timeframe.

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 a number of more invasive actions can be performed to try to rotate the 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 of the procedures can be performed by a midwife at home, and all midwives will have had extensive training on how to do this.

And finally…

So as usual, as bigger mums we’re being told that we have a 3x times the risk / 4x times the risk of something bad happening, but are rarely told that the reality of that risk is a very small 3 or 4 in 1000.

If that risk does materialise, we’re rarely told that in 90% of cases it is resolved by the simple procedure of the mum changing her position.

Obviously the consequences for the baby can be severe, but permanent injury is recorded in just 2 in 10000 births.

Perhaps it is telling that shoulder dystocia accounts for a significant number of medical lawsuits in the UK. Shoulder dystocia claims are the third most litigated obstetric-related complication. Could this be the real reason our choices are being limited?

References

A difficult birth: what is shoulder dystocia? (546.8 KiB)

Green-top Guideline No. 42: Shoulder Dystocia (705.5 KiB)

Maternal Morbid Obesity and the Risk of Adverse Pregnancy Outcome (183.6 KiB)

Outcome of pregnancy in a woman with an increased BMI (12.5 KiB)

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