Scientists have identified a \"fertility switch\" protein which appears to increase infertility if levels are too high and fuel miscarriage if too low. An Imperial College London team took samples from the womb lining of more than 100 women. Writing in Nature Medicine they said women with unexplained infertility had high levels of the enzyme SGK1, while those who miscarried had low levels. One fertility expert said the research offered new avenues for research. About one in six women have difficulty getting pregnant, and one in 100 women trying to conceive experience recurrent miscarriages, defined as the loss of three or more consecutive pregnancies. The Imperial team also carried out mouse studies which found levels of SGK1 in the womb lining decline during the window of time during which they can fall pregnant. When extra copies of the SGK1 gene were implanted into the womb lining, these mice were unable to get pregnant. The researchers say this suggests a fall in SGK1 levels is essential for making the uterus receptive to embryos.