MUMS-to-be who work night shifts are nearly a third more likely to suffer a miscarriage, experts have warned.

Messing with pregnant women's body clocks could be to blame.

Danish scientists found the dangers of losing a baby dramatically increase the more night shift a woman works.

Dr Luise Moelenberg Begtrup, who led the study at Bispebjerg-Frederiksberg Hospital in Copenhagen, said the findings are important given 14 per cent of pregnant women in Europe work at least one night shift a month.

Her team looked at health records of more than 20,000 pregnant women in public services - over a six-year period.

Working two or more late shifts a week ups the risk of miscarriage the following week by 30 per cent, the findings show.

And the risk is greater after a woman's eighth week of pregnancy.

Dr Moelenberg Begtrup said: "The study corroborates earlier findings that night work during pregnancy may confer an increased risk of miscarriage and it indicates a lowest observed threshold level of two night shifts per week.

"The new knowledge has relevance for working pregnant women as well as their employers, physicians and midwifes.

"Moreover, the results could have implications for national occupational health regulations."

Low melatonin levels could affect placenta
Her team also discovered that the risk of miscarriage increased the more night shifts worked and how regular women worked nights.

Scientists are yet to determine a definite reason for the link, but they suspect it's all to do with a pregnant woman's exposure to light and her body clock.

Exposure to light during the night can disrupt a woman's circadian rhythm, which decreases the release of melatonin.

Melatonin is a hormone that preserves the function of the placenta, and is thought to be a crucial part of a successful pregnancy.

Dr Moelenberg Begtrup said: "Studies in humans have found lower levels of melatonin mediated by exposure to light-at-night and with no full catch up during the day among night workers.

"Melatonin plays a role in preserving the optimal function of the placenta.

"Experimental studies have shown the importance of tightly regulated circadian rhythms (body clock), in which melatonin also has a pivotal role, in the maintenance of successful pregnancies."

1 in 4 pregnancies end in miscarriage
In the UK one in four pregnancies end in miscarriage, according to the charity Tommy's.

A miscarriage is the loss of pregnancy during the first 23 weeks, and the main sign is vaginal bleeding often alongside cramping and abdominal pain.

A woman's age, her partner's age and previous pregnancy history can all increase a woman's chance of suffering a miscarriage.

Most happen in the first 12 weeks of pregnancy, and around one in 100 British women experience repeat miscarriages - three or more in a row.

The new findings are published in journal, Occupational & Environmental Medicine.