Giving progesterone to women with bleeding early in pregnancy doesn’t prevent pregnancy loss, except among women who have had a previous miscarriage, a UK study of more 4000 women shows.

For years, progesterone preparations have been used off-label to treat a threatened miscarriage based in part on a decline in hormone levels just before a miscarriage.

That led to a long-practised treatment of giving progesterone even though it was not backed up by good evidence.

The new study of 4153 women treated at 48 hospitals in the UK in the New England Journal of Medicine, provides evidence of when the hormone does or does not work.