A Caesarean section increases the risk by
50-fold that a woman's uterus will rupture during a subsequent
vaginal delivery, research suggests.
A torn uterus can put the life of both the
mother and baby in danger.
US and Swedish researchers found the condition
afflicted nine in every 1,000 mothers who opted to try for
a vaginal birth after a previous Caesarean.
In contrast, the BJOG study found the rate
among women with no history of a Caesarean was just 0.18 per
Many women who have previously had a Caesarean
are offered the option of another, planned Caesarean second
However, around a third of women opt to try
for a vaginal birth to avoid what is a major operation which
carries risk both for the mother and baby.
The findings were based on a study of more
than 300,000 Swedish women by Emory University, Atlanta, and
the Karolinska Institute in Stockholm.
Fourteen of the 274 women who suffered a
torn uterus lost their baby - a death rate of 51 per 1,000.
In contrast, the neonatal death rate among
women who did not develop the condition was just 1.4 per 1,000.
Other risk factors
A prior Caesarean section was not the only
factor which increased risk.
Women who gave birth aged 35 or older were
nearly three times more vulnerable to a uterine tear than
women aged 24 or younger.
Clinically obese women had more than twice
the risk of women who were not overweight.
And inducing labour appeared to double the
risk, compared to labour which began spontaneously.
The researchers suggested the chemicals used
to induce birth weakened previous Caesarean scars, making
them more likely to rip.
Women who gave birth late were discovered
to be more at risk than those who gave birth after a normal-length
pregnancy, regardless of whether they had had a Caesarean
And women who gave birth to babies weighing
at least 4kg were at twice the risk than women whose babies
were less than 4kg.
Researcher Dr Melissa Kaczmarczyk, of Emory
University, said it was important that patients were made
fully aware of the risks, and that those at higher risk were
carefully managed through labour.
Professor Philip Steer, BJOG editor-in-chief,
said: "The rate of Caesarean deliveries continues to increase
in the developed world which means that a growing percentage
of women will experience birth following a previous Caesarean
"Although uterine rupture is a relatively
rare occurrence, the consequences can be devastating.
"The link between a prior Caesarean section
and uterine rupture during subsequent delivery warrants very
careful management of pregnancy and labour so that early signs
of difficulty can be speedily detected."
Mervi Jokinen, of the Royal College of Midwives,
said the study highlighted the fact that a Caesarean carried
a long-term risk to health.
"We believe the Caesarean rate should be
between 10% and 15%, but at present it is 23% in the UK,"
"We should be asking ourselves why the Caesarean
rate is so high."