PRESS ASSOCIATION -- Teenage pregnancy could be "contagious" for girls influenced by their elder sisters who have children while young, new research has suggested.
A team studied the records of thousands of women and their families over decades and found that those with elder sisters who had children in their teenage years were twice as likely to do the same as those without.
The research by British and Norwegian scientists showed that although there is evidence that better education of women leads to lower teenage pregnancy rates, in families with teenage mothers the chances of a younger girl having a child in her teens doubled from one in five to two in five.
The University of Bristol's Professor Carol Propper, who co-authored the study, said: "Previous research has shown that family background and raising the education of girls decreases the chances of teenage pregnancy.
"However, these findings reveal the positive sibling effect (on conception rates) still dwarfs the negative effect of education. These findings provide strong evidence that the contagious effect of teen motherhood in siblings is larger than the general effect of being better educated.
"This suggests that more policies aimed directly at decreasing teenage pregnancy may be needed in order to reduce teen births."
The study - Is Teenage Motherhood Contagious? Evidence from a Natural Experiment - saw Prof Propper work with scientists from the University of Bergen and the Norwegian School of Economics. They analysed census data from 42,606 Norwegian women who were born after the Second World War and their families as they got older.
They chose to look at sister-to-sister relationships because sisters generally spend more time together than with schoolmates or other friends and are therefore likely to be influenced by the behaviour of their siblings. There is also scientific evidence that suggests younger children in families are influenced by the sexual activity of their older brothers and sisters.
They found that the sibling effect is larger for women from poorer backgrounds but gets smaller as the age gap between sisters increases.
Figures released by the Office for National Statistics in February showed that in 2009, the most recent year for which there are records, the rate of conception among UK women aged 18 and under decreased by 5.9%, from 40.7 conceptions per thousand women aged 15-17 in 2008 to 38.3 in 2009. Conception rates for women aged under 20 decreased by 4%.