Young girls whose older sisters were teenage mothers are twice as likely to follow suit, research suggests.
A team of British and Norwegian researchers found the chances of a younger girl having a child in her teens doubled from one in five to two in five in families where there had already been a teenage pregnancy.
In their study, Is teenage mothergood contagious?Evidence from a natural environment, they concluded that new policies may be needed to tackle the 'sibling effect.'
However, they noted that a better education also seemed to result in lower teenage pregnancy rates.
Professor Carol Propper, from the University of Bristol, said: "This suggests that more policies aimed directly at decreasing teenage pregnancy may be needed in order to reduce teen births."