Does controlled ovarian syndrome alter the vaginal and endometrial microbiota?

This study investigated if controlled ovarian stimulation (COS) and progesterone (P) supplementation affects the microbiota (microorganisms found in the human body) of the vagina and uterus (womb).

They found that COS alters the vaginal and uterine microbiota (VUM).

The rate of infertility is increasing worldwide. Many women undergo assisted reproduction (AR) to become pregnant. Controlled ovarian stimulation (COS) is an AR technique. It involves taking medication to trigger the release of oocytes (eggs). In vitro fertilization (IVF) is then performed. Embyros are then transferred to the uterus. These can be transferred immediately (fresh) or frozen and transferred at a later time if the uterus is not yet prepared. Progesterone (P) is a synthetic hormone used to prepare the uterus for implantation of the embryo.

There are many factors that affect IVF success. In many cases IVF failure cannot be explained. The reproductive environment could be one cause. Each body region has a population of bacteria. This is called the microbiota (MB). These includes bacteria that are small and difficult to identify. Many studies have shown the MB is important in health and disease. Biodiversity of bacteria is associated with better health. Bacteria is also found in the vagina and endometrium (uterus lining). The MB of the vagina and endometrium (VEMB) could affect IVF outcomes. It is unclear if COS and P supplementation affect the VEMB in women undergoing IVF. 

This study included 15 women undergoing IVF. All women underwent COS and had fresh embryos implanted. P (600 mg per day) was given for 14 days as vaginal administration for uterine preparation. Women underwent MB analysis before COS and after COS. Samples were taken from the vaginal (V) and endometrial (E) MB. The types of bacteria were compared in samples before and after COS.

The most common bacteria in the vagina was Lactobacillus (LB). LB was reduced in the VMB after COS. LB is a bacteria that protects against the growth of fungi such as Candida (yeast). Vaginal Prevotella (PV) and Escherichia-Shigella (ES) were increased after COS. Increased PV and ES are associated with genital infections.

LB was the most common bacteria in the EMB before COS and remained common after COS. Higher levels of PV and Atopobium (A) were idenified in the EMB after COS. Increased A is also associated with genital infections. Biodiversity (more types of bacteria) was higher in the VMB and EMB after COS. 

The authors concluded that COS and P supplementation modify the VEMB. The authors suggest that frozen embryo transfers may be considered if the VEMB is altered.

This was the first study of this kind. The number of patients in this study was low. Larger studies are needed to confirm these findings.