Microbiomes affects a woman’s chances of getting pregnant

Microbiomes, namely the balance of bacteria, have a direct impact on the way to the desired pregnancy – a new study

Vaginal and endometrial microbiomes are the factors that affect a woman’s reproductive function. A new study by JBRA Assisted Reproduction, which examines the outcomes of assisted reproductive technologies (ART), says that certain microbial profiles are associated with better conception rates.

What the study is about

The researchers studied factors that influence the outcome of assisted reproductive therapy, in particular reproductive tract infections.

The vaginal microbiome consists of several beneficial bacteria such as Lactobacillus. When the number of these bacteria decreases, accompanied by an increase in anaerobes such as Gardnerella vaginalis, bacterial vaginosis (BV) can occur. It affects nearly 20% of infertile women and can be caused by both G. vaginalis and Atopobium vaginae.

Scientists have investigated how the pregnancy rate with In Vitro Fertilization (IVF) is affected by the balance between numerous pathological bacteria. They include Gardnerella, Enterococcus, Enterobacteriaceae, Streptococcus and Staphylococcus, and Lactobacillus. The researchers designed a prospective study based on vaginal and endometrial microbiome samples from 35 ART patients who underwent embryo transfer at a single center between February 2019 and March 2020.

All embryos were of good quality, and embryo transfer (ET) was performed if the endometrial thickness was at least 8.0 mm on day 15 of the cycle. All microbiome samples were collected between the eighth and tenth days of the menstrual cycle. A total of 34 and 33 vaginal and endometrial samples were included in the study, respectively.

How microflora affects conception

Of the 34 IVF procedures, 21 resulted in pregnancy, 17 in live births and four early miscarriages. Among pregnant women, high levels of Lactobacillus were found in both vaginal and endometrial samples, compared to high levels of pathogenic bacteria in non-pregnant samples.

Thus, a favorable balance of Lactobacillus bacteria in the endometrium and vagina was associated with a higher proportion of women who became pregnant. This remained true after excluding those who received antibiotics.

Significantly more women became pregnant when Lactobacillus and pathogenic bacteria counts were high and low, respectively. And significantly more women did not become pregnant when Lactobacillus and pathogenic bacteria counts were low and high, respectively.


The researchers concluded that Lactobacillus predominates in the endometrium and vaginal microbiomes because its presence prevents pathogenic bacteria from entering the uterus.

According to them, further research is needed to find out the mechanisms by which the endometrial microbiome affects pregnancy. This is necessary to study methods of correcting dysbiosis, in particular, whether to enhance the growth of Lactobacillus, or the use of antibiotics to suppress the excessive growth of pathogens.


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