Jules Hillier, the deputy chief executive of the charity Brook, said: “The researchers in Norway in conjunction with the University of Bristol have claimed that teenage girls are most likely to become pregnant if their elder sister became a teenage mum. It is well known that teenage pregnancy is influenced by family background and level of education. The Norwegian study aimed at exploring teenage pregnancy as it relates to the influence of sisters on each other. The study looked at births rather than conceptions. The data, which consisted of children born between 1947 and 1958, was compared to families from a similar background from different regions of Norway. The study of 42,000 Norwegian teenage girls showed that sisters of similar age or low financial status had a greater chance of becoming pregnant as teenagers. The effect of sisters on each other has been described as “the contagious effect of teen motherhood”, according to one of the researchers, Professor Carol Propper, who also said: “Two groups were particularly vulnerable – those in low income households and sisters close in age.” Professor Propper said an elder sister with a baby could also influence the decision to keep a baby. However, any “sister effect”, Propper stated, would dissipate as the age gap widened because the sisters would be on “different life trajectories”, whereas those of similar ages would have similar social circles.The report found that: “Sisters generally spend more time together than schoolmates or friends and so sisters are likely to be influenced by the behaviour of their siblings.” The researchers said the probability of the younger sister having a teenage pregnancy went from one in five to two in five if the elder sister had a baby as a teenager.She elaborates: “Social and economic deprivation and poor education all impact hugely onto it and we already know that being the daughter of a teenage mother is one of the contributing risk factors towards teenage pregnancy.ere are links between low aspirations, deprivation and teenage pregnancy, but there are also a whole range of measures that need to be in place to reduce teenage pregnancy rates such as comprehensive sex and relationships education and easy access to sexual health services.”The Family Planning Association noted that the results may not necessarily apply to the UK but were still of interest.