Scientists have identified an enzyme which they believe increases the risk of infertility if it is too high and miscarriage if too low.
Researchers from Imperial College London took samples from the womb lining of more than 100 women. They found women with unexplained infertility had high levels of the enzyme SGK1, while those who miscarried had low levels.
The team also looked at how the enzyme affected pregnancy in mice.
Prof Jan Brosens, who led the research at Imperial's Institute of Reproductive and Developmental Biology, said: "Our experiments on mice suggest that a temporary loss of SGK1 during the fertile window is essential for pregnancy, but human tissue samples show that they remain high in some women who have trouble getting pregnant.
"I can envisage that in the future, we might treat the womb lining by flushing it with drugs that block SGK1 before women undergo IVF."
Their findings were published in the journal Nature Medicine.