A newly published study in The Lancet Obstetrics, Gynaecology & Women’s Health reveals that imbalances in the seminal microbiome are associated with higher rates of pregnancy loss and lower live birth rates following fertility treatments. According to lead author Ida Behrendt-Møller, the research marks a departure from historical reproductive studies by examining male seminal fluid alongside female microbial ecosystems to better understand unexplained infertility.
The Seminal Microbiome and Pregnancy Outcomes
Infertility affects approximately 48 million couples worldwide, and a substantial share of these cases lack a clearly identified medical cause. To investigate whether microbial communities play a role, researchers followed couples undergoing in vitro fertilization (IVF), intracytoplasmic sperm injection (ICSI), and treatments for recurrent pregnancy loss over a period of nine years. The investigation examined three distinct microbial ecosystems simultaneously: the vaginal microbiome, the female intestinal microbiome, and the male seminal microbiome.
According to the findings, semen samples displaying a bacterial profile similar to bacterial vaginosis took longer to achieve a live birth and carried an elevated risk of pregnancy loss. Co-author and bioinformatician Pernille Neve Myers noted that because couples routinely transmit infections during sexual activity, they may also share beneficial or pathogenic bacteria capable of influencing reproductive success.
Evaluating Microbial Ecosystems in Fertility
Paradoxically, the vaginal microbiome—the most studied system to date—did not show a consistent association with live birth rates in this cohort. However, Ida Behrendt-Møller emphasized that this lack of direct association does not rule out a supporting role for vaginal bacteria in reproductive health. Previous scientific literature links certain vaginal bacterial shifts to heightened risks during embryo implantation, potentially by triggering local immune responses or infections.
The research team underscored that the current findings demonstrate associations rather than direct causality. Seminal microbes could theoretically impact reproductive outcomes directly through sperm function and fertilization. Because recruiting participants undergoing emotionally challenging fertility treatments is difficult and genetic sequencing analyses remain costly, the study relied on two independent cohorts comprising more than 350 women and nearly 200 men; the women were aged between 18 and 41 and their male partners were 18 or older.
Frequently Asked Questions
What did the Lancet study investigate?
According to the published research, the study examined the relationship between the seminal, vaginal, and female intestinal microbiomes and their impact on miscarriages and success rates in fertility treatments.
How does the seminal microbiome affect fertility treatments?
The study found that imbalances in seminal bacteria resembling bacterial vaginosis are associated with a higher risk of pregnancy loss and a lower probability of achieving a live birth following reproductive treatments like IVF.
Did the study prove that bacteria directly cause infertility?
Worth a look