A treatment that prevents premature births in single pregnancies may be ineffective in women expecting more than one child, a study has shown.
The study, led by a University of Edinburgh researcher, suggests an underlying difference between the way in which premature births occur in women with single and multiple pregnancies.
The findings published in the The Lancet could help inform improvements in treatment to prevent premature births in women expecting more than one child and help researchers understand how the process of premature labour may be different.
The study looked at nearly 500 women around the country expecting twins, which account for more than 98 per cent of multiple births in the UK.
Half of the women were given progesterone gel - a hormone which helps protect the lining of the womb - while the other half were given a dummy version. The treatment has been shown to reduce early births in women expecting one child considered at high risk of early labour, including those who had previously given birth prematurely.
However, researchers found that contrary to singleton pregnancies, the hormone gel did not reduce rates of premature births.
Professor Jane Norman, director of the Tommy's Centre for Maternal and Fetal Health Research at the University of Edinburgh, said: "While the study looked at twins, it suggests that the biological process of premature births in women with multiple births is different for that than in women expecting one child.
"Understanding the differences between what happens in premature births in singleton and multiple pregnancies can help us improve treatments and also address the higher incidence of premature labour in multiple pregnancies."
Professor Norman, who is also a consultant obstetrician at the Simpson's Centre for Reproductive Health at the Royal Infirmary of Edinburgh, said that around 20 per cent of multiple pregnancies resulted in pre-term delivery before 34 weeks compared to two to three per cent of pregnancies for women expecting one child
Multiple pregnancies accounted for 1.6 per cent of all births in the UK in 2007, but rates of stillbirths and neonatal mortality are between three and eight times higher than in singleton pregnancies.