Womb rupture is rarer than previously thought

The risk of womb rupture in pregnancy and labour is very small and lower than previously thought, according to a new Oxford University study.

Uterine or womb rupture is a rare complication where the womb wall tears open, and occurs most often in labour when the womb is under pressure and contracting. Although it is rare, it can be very severe and even life-threatening for mother and child.

Most cases of womb rupture happen in women who have had a caesarean section before. However, the Oxford researchers found that the risks remain small even in women planning a normal birth after a previous caesarean – though they are higher than those that opt for another caesarean.

They say that there is no need to change current guidance on birth after a previous caesarean, which is that women should be able to plan the birth they feel most happy with, after discussing the risks and benefits of caesarean and vaginal birth with their doctors and midwives.

Professor Marian Knight of the National Perinatal Epidemiology Unit at Oxford University, who led the study, said: 'Womb rupture is a severe but thankfully very rare complication. We found that many of the hospital maternity units across the country don’t even see one case a year. Among women who’ve had a previous caesarean, there is a higher risk for those planning a normal birth rather than another caesarean. But the risk remains very small, occurring in just 0.2% of such pregnancies.

'Given that this figure is lower than many previous estimates, there should be no extra reason to worry. We see no reason to change current advice that women can choose how they would like to have their baby after a previous caesarean, and that in general a vaginal birth should be possible.'

The study is published in the journal PLoS Medicine and was funded by the UK charity Wellbeing of Women and a National Institute for Health Research (NIHR) Programme Grant. 

The Oxford researchers found that womb rupture occurs in just 2 in 10,000 pregnancies in the UK – confirming that this is a rare complication. The vast majority of cases (139 out of 159) were in women who’d had previous caesarean sections.

Womb rupture is still rare among women who have had a previous caesarean section and plan to have a normal birth at 21 per 10,000 pregnancies. But this is higher than in those who elect for another caesarean section, where the incidence is 3 per 10,000 births.

Professor Knight added: 'Womb rupture is not the only complication that should be taken into account when planning births following a previous caesarean delivery. These findings need to be considered alongside other small risks and benefits of either vaginal or caesarean birth. This is why it should be an individual choice for women in consultation with their midwives and doctors.

'While there may be an increase in risk of womb rupture in planning normal birth after a caesarean, electing to have another caesarean can have other associated risks. C-sections are very safe operations but there are small short-term risks of infection or blood clots, there is the often longer recovery period and there are consequences for subsequent births. For example, the more caesareans you have, the more likely hysterectomy and womb rupture becomes.'

The researchers compared outcomes for the womb rupture cases with those for a control group of 448 women giving birth after previously having had a caesarean section.

Other factors that were associated with increased risk of womb rupture were the number of previous caesarean sections the mother had had; a short time since the previous caesarean delivery; and induction of labour.

Professor Knight explained what can be taken from these findings: 'For women who have had a caesarean section, what may be the most useful thing to know is that you will have a lower risk of womb rupture if you wait at least 12 months before conceiving again.

'Obstetricians and midwives can now be aware that, although rare, inducing labour, or using oxytocin to strengthen contractions, is associated with greater risk of womb rupture. We now have a good measure of the size of that risk, enabling this information to be put into perspective when discussing birth options with women.'