Twins born through fertility treatment and their mothers are far more likely to suffer problems than single births, new studies show.
Until recently fertility clinics implanted several embryos to increase the chance of conception, but the practise led to women regularly having more than one child.
Now new research has shown that even giving birth to twins through fertility treatment, such as IVF, substantially increases the risk to both mother and children.
They were five times more likely to need a Caesarean section and 10 times more likely to be born prematurely.
Prof Barbara Luke, at Michigan State University, looked at the birth outcomes for 6,000 single pregnancies and 2,500 twins.
"And what we found was that being a twin versus a singleton at birth increased the risk for all outcomes except for of course large for age," she said.
Multiple pregnancy is the single biggest risk of fertility treatment, according to the Human Fertilisation and Embryology Authority.
It increases the risk of stillbirth, neonatal death and disability in children born. It also increases the risk of dangerous complications to... see more