Fertility scientists say they have made a "crucial breakthrough" in understanding why some women have repeated miscarriages.
There has been debate about whether giving steroids would help women who have lost multiple pregnancies.
University of Warwick researchers say they have now shown how low steroid levels lead to some miscarriages.
Experts said identifying the right women for treatment would be key, as steroids may make the problem worse.
More than one in seven pregnancies end in miscarriage.
Many women will successfully have a baby at the next attempt, but recurrent miscarriage - losing three or more pregnancies in a row - affects one in 100 in the UK.
Prof Siobhan Quenby from the University of Warwick said: "It causes incredible psychological distress and anguish.
"The routine advice in the UK is if blood tests identify no cause then there's no treatment, that's terribly unacceptable to patients."
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