• The scientists found the women having regular miscarriages were giving their partners significantly less fellatio.
• The study was published in the Journal of Reproductive Immunology.
Women who regularly give their male partner oral sex may be less likely to suffer recurrent miscarriages, scientists claim.
Researchers believe swallowing semen strengthens a pregnant woman's immune system in a way which makes foetuses more likely to grow healthily.
This could be, they say, because it contains hormones and proteins from the man's body, to which it could be useful for the mother to build up a tolerance.
Vaginal exposure to semen – so unprotected sex – could also play an important role in a couple trying to conceive, but semen may be better absorbed in the gut.
Researchers from Leiden University Medical Centre in the Netherlands tested their theory comparing the pregnancy history and oral sex habits of 234 women.
They acknowledged the study was small and did not provide evidence that swallowing sperm was leading to the lower miscarriage rate.
But they believe their results are strong enough to suggest a link between the two and warrant more research.
Some 97 of the women had suffered from recurrent miscarriage – a condition in which a woman has three or more miscarriages in a row.
The condition is thought to affect around one in 100 women in the UK and may be triggered by genetic or hormonal problems, or infection. Many cases are unexplained.
In their study, the scientists found the women having regular miscarriages were giving their partners significantly less fellatio.
While 73 per cent of women in the non-miscarriage group regularly gave oral sex, only 57 per cent of those in the miscarriage group did.
'Oral exposure to seminal fluid seems to... influence pregnancy outcome in a positive way,' the researchers wrote.
They added: 'Our results suggest an association between less oral sex and the occurrence of recurrent miscarriage.'
By building up the mother's tolerance to substances from the man's body, the parents could give a foetus – half-made of the father's DNA – a better chance of thriving.
This could, the theory explains, make the mother's immune system less likely to reject the baby and lead to its death.
Past research may have focused too much on the mother's own biology, the scientists suggested, instead of the impact of the father's bodily fluids.
The study was published in the Journal of Reproductive Immunology.