AN imbalance of bacteria in men’s semen may raise the risk of a miscarriage, a study suggests.

Researchers behind the five-year project tracked 353 women and 191 of their male partners who were undergoing fertility treatment or had experienced recurrent pregnancy losses in Denmark.

An issue with the bacteria in men’s semen has been linked to a higher chance of miscarriage, a study has suggested Credit: Getty

The issue could also give couples a lower chance of conceiving Credit: Getty

About a quarter of the male partners had a bacterial imbalance in their semen, analysis showed.

Among couples undergoing IVF or intracytoplasmic sperm injection (ICSI), 57 per cent of those with this imbalance went on to have a baby.

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By comparison, 85 per cent of those without the imbalance had a baby.

Pregnancy loss was also more common when the man had the imbalance, affecting roughly one in five more couples than when it was not detected.

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Writing in the journal The Lancet Obstetrics, Gynaecology, & Women’s Health, researchers from the University of Copenhagen said that imbalances in men’s semen are “overlooked and potentially treatable risk factors for infertility and recurrent pregnancy loss”.

They added: “Current management of infertility focuses largely on female-directed interventions.

“Incorporation of couple-level microbial assessment might represent a novel approach for targeted therapeutic strategies.”

In the study, the researchers also found that an imbalance in gut bacteria in women was linked to a lower chance of becoming pregnant through fertility treatment.

This imbalance was also linked to taking longer to conceive, although it was not linked to miscarriage.

The study stressed that an imbalance in the vaginal bacteria was not clearly linked to either infertility or pregnancy loss.

The authors added: “Although the vaginal microbiome has been studied extensively in relation to fertility, the gut and seminal microbiome – related to semen – have been largely overlooked”.

The microbiome is the combination of microorganisms – including bacteria, viruses, parasites and fungi – living inside our body.

It comes after a study published last week found that hospital admissions in England for ectopic pregnancy have risen by four per cent every year since 2021.

Authors of the study – published in The Lancet Regional Health – Europe – suggested that this increase may reflect demographic changes such as rising maternal age.

They said other factors for this increase could include increased rates of risk factors such as obesity and disruption to hospitals and maternity services due to Covid.