Despite high-tech, super-expensive IVF technology embryo implantation often fails. And the reason why often remains unclear. But, there’s a growing interest in the way bacteria influence the likelihood of implantation and early results indicate that switching up the body’s microbiota (bug-balance) may improve fertility.

Each of us is host to an incredibly large population of bacterial cells, in fact bacterial cells out number our body cells by a long way. Importantly, bacterial communities which inhabit the reproductive system and especially the uterus may influence implantation.

Historically the bacterial balance within the uterus has not been deeply considered as a factor in embryo implantation, but newer research (1) indicates that the endometrium hosts it’s own specialized microbiota which may vary from the microbial communities found in the rest of the reproductive system.

A 2016 study examined bacteria from uterus and reproductive system in thirteen fertile women at various stages throughout their cycles and determined that uterus fluids may be predominated by lactose-fermenting bacteria such as Lactobacillus or non-lactose-fermenting organisms.

A further component of this study (1) looked at how the balance of uterine bacteria may influence embryo implantation.

Thirty five infertile women who were undergoing in-vitro fertilization (IVF) underwent an endometrial receptivity array test to confirm endometrial receptivity AND had their uterine bacterial balance analyzed.

The results of this extra part of the study were super-interesting. The presence of non-lactose-fermenting bacteria in uterus fluid was linked with a big dip in implantation rates.

Women with predominantly NON-lactose-fermenting bacteria had lower implantation rates (23.1%) compared with women with a predominantly Lactobacilli focused uterine microbiota (60.7%).

Ongoing pregnancy rates in women with predominantly lactose-fermenting bacteria were 58.8% (versus 13.3%) and live birth were 58.8% (versus 6.7%).

"Our results demonstrate the existence of an endometrial microbiota that is highly stable during the acquisition of endometrial receptivity."

"However, pathological modification of its profile is associated with poor reproductive outcomes for in vitro fertilization patients."

Another 2016 study (2) examined how the female reproductive microbiota may shape pregnancy success after IVF. In this study one hundred and thirty women who were undergoing IVF underwent qPCR testing to chart their microbiota.

An abnormal microbiota was present in twenty eight percent of women, and of the eighty-four patients who completed their IVF cycles the overall clinical pregnancy rate was 35%.

But interestingly, in women with an abnormal bacterial balance in the reproductive tract the clinical pregnancy rates was only 9%.

It is possible that female-specific probiotics and a diet rich in lactose-fermenting bacteria may help to shift the reproductive tract microbiota in the right direction, and the steps you take to cultivate a healthy microbiota may also improve fertility.

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(1) Am J Obstet Gynecol. 2016 Dec;215(6):684-703. doi: 10.1016/j.ajog.2016.09.075. Epub 2016 Oct 4. Evidence that the endometrial microbiota has an effect on implantation success or failure. Moreno I1, Codoñer FM2, Vilella F3, Valbuena D4, Martinez-Blanch JF2, Jimenez-Almazán J5, Alonso R5, Alamá P6, Remohí J7, Pellicer A8, Ramon D9, Simon C10.

(2) Hum Reprod. 2016 Apr;31(4):795-803. doi: 10.1093/humrep/dew026. Epub 2016 Feb 23. Abnormal ******* microbiota may be associated with poor reproductive outcomes: a prospective study in IVF patients. Haahr T1, Jensen JS2, Thomsen L1, Duus L3, Rygaard K4, Humaidan P5.