Can probiotics improve fertility?

This review looked at whether probiotics can improve fertility. It found that probiotics improve sperm quality, and it is not clear whether probiotics improve pregnancy rates following in vitro fertilization (IVF).

For every human cell in a person’s body, there are 10 microbial cells living on the skin, in the gut, and on every other surface of the body. These bacteria, fungi, and other microorganisms in the body form the microbiome. The microbiome affects everything from how we digest food to how our immune system develops.

The reproductive tracts of both men and women also have microbiomes. A healthy vaginal microbiome contains primarily lactobacilli, which keep the vagina acidic. An acidic environment discourages harmful microbes from ascending into the uterus. During childbirth, these lactobacilli also form the first microbiome of the newborn and prepare it to digest milk. When there are fewer lactobacilli, other potentially harmful species can develop. This is known as a non-lactobacilli-dominated microbiome (NLDM).

Women with abnormal reproductive microbiomes have higher rates of infertility and are more likely to have pregnancy complications including infection and preterm birth. The infertility treatment IVF has higher pregnancy rates for women with predominantly lactobacilli in the lining of their uterus. The male reproductive microbiome also influences fertility, although it is not as well studied.

Probiotic therapy consists of applying healthful live bacteria either orally or vaginally. It is not clear whether probiotics can improve IVF outcomes.

This review included four studies. Two studies examined vaginal probiotics prior to IVF. The other two studies gave oral probiotics to the male partners prior to IVF.

Antibiotics and probiotics successfully treated 53% of women with NLDM. One study found a trend toward higher pregnancy rates for women whose NLDM was treated, but this could have been due to chance. Probiotics alone did not improve NLDM or pregnancy rates. There was no difference in the number of eggs retrieved following vaginal probiotics, either with or without antibiotics.

Oral probiotics significantly improved sperm concentration (28.3 vs. 15.2 million per 39 mL) following six weeks of treatment. Six months of oral probiotics also improved sperm motility (movement; 28.6% vs. 6.4%). There was also a significant improvement in the amount of DNA fragmentation (damage to the genetic material of the sperm).

This study found that oral probiotics can improve sperm quality. It also found that antibiotics and probiotics can treat NLDM.

More and larger studies are needed, particularly on whether treatment for NLDM can improve pregnancy rates.