While pregnant women who had previously had a miscarriage, an additional dose of progesterone helps them continue to have a successful pregnancy, scientists say.
Progesterone is produced naturally in the female body and plays an important role in the menstrual cycle and in the maintenance of the early stages of pregnancy.
A study found that women who had one or more spontaneous abortions and who had early bleeding in their next pregnancy could benefit from additional doses of the hormone.
Researchers at the University of Birmingham reported that about 4,700 babies could be born, which would otherwise be buried annually in the UK.
The study did not show that progesterone can help all women who have suffered bleeding in early pregnancy, but it has been found that they are beneficial to those who have previously been infected.
In a major study of this kind, 4,153 pregnant women who presented bleeding in early pregnancies in 48 British hospitals were randomly assigned from a computer to one of the two groups.
The first group, of 2,079 women, received 400mg of progesterone twice daily as a vaginal pessar. The latter, out of 2,074, was given placebo.
About 780 women who previously had one or two abortions were progesterone in the study.
About 591 (76%) had a live birth, compared with 534 women from 738 in the placebo group (72%).
The effect of progesterone was greater in women who suffered three or more spontaneous abortions, with an increase of 15% in the live birthrate in the progesterone group compared to those who received placebo.
Out of 137 women with three or more previous abortions, 98 (72%) had a live birth, compared with 57% (85 out of 148) women in the placebo group.
Arri Coomarasami, a professor of gynecology at the University of Birmingham and director of the Tommy's National Center for Research, says: "The role of progesterone in women with bleeding in early pregnancy has been studied and debated for about 60 years, but what we did not previously is a high quality proof ".
He added: "Our conclusion that women who are at risk of miscarriage due to instantaneous bleeding in pregnancy and a history of previous miscarriage could benefit from treatment with progesterone has huge consequences for the practice.
"This treatment can save thousands of babies who may have been otherwise miscarried for miscarriage."
The PRISM trial was funded by the National Institute of Health Research (NIHR) and published in the New England Journal of Medicine.