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Sue Radford, the mum of Britain’s biggest family, is planning for the birth of her 22nd child.

And while the Radfords may be a little unusual in having quite so many kids, a surprising number of us are having more than the national average of 1.75 in a lifetime. In fact, according to the ONS, 70,000 families had more than five children in 2017.

So what are the effects on a woman’s body when she gives birth multiple times? Is it damaging – or even, dangerous?

Well, it’s not always as simple as assuming that the more children you have, the greater the effects, according to consultant obstetrician Dr Daghni Rajasingam. She told HuffPost UK women’s bodies respond very differently to pregnancy and childbirth – and this can depend on factors including genetics, age, weight and unknown complications.

“Recovery can be very varied based on whether a woman has had a vaginal or caesarean birth, whether it was a multiple birth (such as twins) and whether there was any tearing,” she said.

But some doctors warn that as the number of births increases, so does the potential harm to the mother – and the child. One doctor said the more pregnancies a woman has, the greater the risk of a negative outcome. Doctors worry these women may haemorrhage after delivery, said Dr. Lois Brustman, an associate professor of obstetrics and gynaecology at Columbia University.

This is because the uterus – which is a muscle – can get stretched more each time a woman is pregnant. “As a result,” she told LiveScience, “after a woman has had many pregnancies, the muscle has a hard time contracting after the placenta separates. This creates a risk of bleeding.” She also said scar tissue from previous pregnancies can cause problems with the placenta, including the risk of premature birth.

Dr Dorothy Shaw, a clinical professor in obstetrics and gynaecology at the University of British Columbia in Canada, told CNN there was a “clear connection” between countries that have a high fertility rate, where women have six to seven children, and maternal mortality rates.

“Once you get past two to three children, the risks increase for complications.” - Dr Dorothy Shaw, a clinical professor in obstetrics and gynaecology

Shaw believes this could be linked to ‘maternal depletion syndrome’ – where the mother doesn’t recover from the loss of key nutrients between pregnancies – and uterine rupture [tearing of the uterus]. “Once you get past two to three children, the risks increase for complications,” she added.

In 2014, a study by the University of Texas Southwestern Medical Center found women who have four or more children double their risk of heart disease. At the time, lead author Dr Monika Sanghavi said while the findings added to the body of evidence that changes associated with pregnancy may provide insight into a woman’s future cardiovascular risk, it was “not a recommendation for women to only have two or three children” and deserves further attention. More research is needed, they suggested.

So how many children is it possible – and safe – for a woman to have in a lifetime? The answer isn’t clear-cut. “I’m not sure the uterus has a limit,” said Brustman.

If you’re planning to have a big family, there are things you can do to protect your body, says Dr Rajasingam, who’s also a spokeswoman for the Royal College of Obstetricians and Gynaecologists.

“We recommend that women maintain good health, eat a balanced diet, avoid fatty and sugary foods, and exercise regularly before, during pregnancy and after birth,” she says.