Doctors may be able to predict which women are at high risk of miscarriage by measuring their hormones, say researchers.
Scans can check foetal health
Women likely to miscarry tend to have lower blood levels of hormones produced by the placenta, scientists at University College London found.
In the future, it might be possible to correct the cause of these imbalances to prevent miscarriage, experts hope.
Recurrent miscarriage - three or more in a row - affects one in 100 women.
Doctors had previously noted that levels of a certain hormone, called inhibin A, were lower in failed IVF pregnancies than in successful IVF pregnancies.
Professor Eric Jauniaux and his team, with funding from the Wellcome Trust, set out to investigate whether this hormone and others produced by the placenta might be useful markers of early pregnancy loss.
They took blood samples from 37 pregnant women, including women with a history of unexplained recurrent miscarriages, women with no history of miscarriage and women who had had one miscarriage in the past.
At as early as six weeks' gestation, levels of three placental hormones - inhibin A, hCG and oestradiol - were up to four times lower in the women who went on to miscarry compared with the women who subsequently had a live birth.
These hormones are known to be critical for the embryo's nourishment and development.
Professor Jauniaux said: "If we are able to identify these clear hormone variations early enough, we believe there is a real window of hope for the development of preventative therapies for these patients."
Work by other researchers supports the idea that inhibin A might be a good marker for predicting pregnancy outcome.
But a team of Australian researchers found it was not helpful.
Professor Jauniaux' team acknowledge that more research is needed and are planning further investigations involving many more women.
A spokeswoman from the Miscarriage Association said: "We really welcome this research, particularly because it might lead to the development of treatments to prevent recurrent miscarriage.
"Although it is important to pick up miscarriages earlier, that is nowhere near as important as being able to possibly develop treatments that might prevent it.
"I know it's early days yet, but it does look a promising line of research.
"Recurrent miscarriage is very distressing and it is not uncommon. This type of research gives women who suffer from recurrent miscarriage real hope for the future."