Bacterial imbalance in semen can become a risk factor for infertility, according to a study published in The Lancet Obstetrics, Gynaecology, & Women’s Health. The research, led by the Copenhagen University Hospital, analyzed the intestinal and vaginal flora of women and the semen of men to subsequently track each couple’s pregnancies and childbirths over time.
Bacterial imbalance in semen and fertility
Clocking in as the central finding was that bacterial imbalance in semen was associated with a lower probability of achieving a live birth and with more miscarriages. In parallel, the alteration of the women’s intestinal flora also showed a relationship with fewer pregnancies through fertility treatments and a longer time to conceive.
This result reinforces a line of research that in recent years has focused attention on the reproductive microbiome, that is, the set of microorganisms that coexist in the reproductive system. In the male case, several previous studies have linked bacteriospermia and seminal dysbiosis to poorer motility, lower concentration, and alterations in sperm morphology.
What bacterial imbalance in semen means
The bacterial imbalance in semen does not in itself imply a serious infection, but it can reflect inflammation, oxidative stress, or the presence of bacteria that alter seminal quality. Scientific reviews cited in medical literature point to associations with microorganisms such as Escherichia coli, Enterococcus faecalis, Staphylococcus aureus, Prevotella, and Ureaplasma urealyticum.
In clinical practice, bacteriospermia has been described as relatively frequent and, in some studies, related to up to 15% of male infertility cases. However, the evidence is not uniform: other research has found bacteria in the semen of fertile men without relevant changes in seminal quality.
What this study contributes
The novelty of the work lies in analyzing the couple as a reproductive unit and not just the semen separately. This allows us to observe that bacterial imbalance in semen and the alteration of the female microbiota could act together on the probability of pregnancy.
The study does not claim that every bacterium in the semen causes infertility, but rather that certain patterns of imbalance are associated with worse reproductive outcomes.
For specialists, the value of findings of this type lies in opening the door to more precise tests, microbiological evaluation, and targeted treatments when there are signs of infection or sperm alteration.
In a region where infertility remains a little-discussed problem, bacterial imbalance in semen adds an important clue: male reproductive health also depends on microbial balance, and that detail can make a difference in the outcome of trying to conceive.
The clinical monitoring of couples with conception problems could more frequently incorporate the study of bacterial imbalance in semen, especially when there are recurrent miscarriages, fertility treatment failures, or persistent sperm alterations.
