A girl whose older teenage sister becomes pregnant is more likely to become pregnant herself, British and Norwegian researchers revealed in a new study. The closer the age gap the higher the risk, they added. Also, if the girls come from a poorer background the likelihood that the younger sibling becomes pregnant as a teenager too is higher.

Professor Carol Propper from the University's Centre for Market and Public Organisation and colleagues from the University of Bergen and the Norwegian School of Economics set out to determine what impact peer effect might have between sisters. They gathered data from the Norwegian census which included 42,606 women who were born after WWII.

They found that the peer effect on the younger teenage sister was considerable regarding becoming pregnant as a teenager. A teenage girl whose older sister became pregnant during her teens is twice as likely to become pregnant herself, compared to girls whose sisters did not become pregnant during their teens.

The probability wears off the larger the age gap between the two girls is, the researchers found.

However, in low-income households the peer effect was found to be greater.

The study also revealed that academic level is linked to the probability of becoming pregnant as a teenager - the greater the education the lower the likelihood. However, the impact of a teenage sibling becoming pregnant appears to be stronger than the impact of education.

Professor Propper 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 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."

Written by Christian Nordqvist