ART and embryo transfer: is your vaginal flora one of the keys to success?
Could lactobacilli, the guardians of vaginal health, also boost the chances of getting pregnant after a frozen embryo transfer? This is suggested by a US study 1 that also links this trend to ethnic origin.
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About this article
When talking about
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Infertility
Disorder of the male or female reproductive system defined by the inability to achieve pregnancy after 12 months or more of regular unprotected sexual intercourse.
https://www.who.int/news-room/fact-sheets/detail/infertility
)
and ART (assisted reproductive technology), we often think of a journey filled with hope, expectation... and sometimes disappointment. Among the proposed techniques, frozen embryo transfer consists of placing in the uterus an embryo previously conceived in the laboratory through
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In vitro fertilization (IVF)
A medical assistance technique for procreation where fertilization takes place in the laboratory, in a test tube (“in vitro”), and not in the woman’s uterus: eggs retrieved from the woman after hormonal stimulation are placed in a nutrient solution with sperm collected from the man. The embryos thus conceived in the laboratory will then be transferred to the future mother’s uterus via the vagina. If an embryo implants, the pregnancy begins.
https://www.service-public.fr/particuliers/vosdroits/F31462
https://medclinics.com/fr/fiv/
https://www.fiv.fr/fecondation-fiv/
)
, then frozen and subsequently transferred.
17,5 % Infertility is common worldwide, with a lifetime prevalence estimated at 17.5%.
The aim? To achieve embryo implantation, thus initiating the eagerly awaited pregnancy. However, in reality, it’s not automatic: only 41% of egg retrievals result in pregnancy in women under 35.
+52% pregnancies with Lactobacilli
In this context, every little bit helps. And it seems that help might come from the microbiota, already involved in female and male infertility and in miscarriages. Could it also promote embryo implantation in cases of ART? A study conducted in the United States focused on 87 women who underwent frozen embryo transfer. It analyzed their vaginal microbiota at the time of transfer to see if it influenced the outcomes.
Did you know ?
Although in vitro fertilization (IVF) success rates have gradually improved, the rate of live births per egg retrieval remains around 41% for women under 35 and progressively decreases with maternal age.
Result: among women whose vaginas were largely dominated by lactobacilli, particularly Lactobacillus crispatus or L. gasseri species, chances of pregnancy were 52% higher! Two-thirds of the women who became pregnant after embryo transfer had more than 80% lactobacilli in their vaginas.
Conversely, women whose microbiota hosted more opportunistic bacteria like Enterobacteriaceae or Streptococcus were less likely to become pregnant. However, neither the richness nor the diversity of the flora was associated with ART success: it is the type of bacteria that makes the difference.
An explanation for ethnic disparities?
Another interesting point addressed by the study: ethnic disparities. The authors made sure to include Hispanic women, who represent 19% of the US population but are often missing from studies.
The results show they had lower pregnancy rates. And their vaginal microbiota is less often dominated by beneficial Lactobacillus compared with non-Hispanic white women. A link worth exploring, which could partly explain lower rates of successful frozen embryo transfer in the Hispanic community.
