Scientists are blaming a 'faulty fertility switch' for infertility and miscarriage.
Researchers have found that high levels of a protein called SGK1 can cause infertility, whilst women with low levels are more likely to suffer a miscarriage.
The results of the study will lead to further research into treatments to ensure mums and mums-to-be have the right levels of the protein in the womb.
Tissue samples were taken from 106 women by experts at Imperial College London in the study, which was undertaken in a bid to help identify which women may be at risk of abnormalities before they get pregnant.
In tests on mice, the research team found levels of SGK1 in the womb lining declined during the period when pregnancy could occur, but when extra copies of the SGK1 gene were implanted into the womb lining, the mice were unable to become pregnant.
The scientists say this suggests a fall in SGK1 levels is necessary for making the womb receptive to embryos.
Lead researcher Madhuri Salkertold reporters: "In the future, we might take biopsies of the womb lining to identify abnormalities that might give them a higher risk of pregnancy complications, so that we can start treating them before they get pregnant."
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