Effect of laparoscopic niche resection on vaginal microbiota and its relation to pregnancy rate

Objective: To study the impact of a laparoscopic niche resection on vaginal microbiota in relation to pregnancy rate. Methods: A explorative prospective cohort study that included women with a large niche (residual myometrium ≤ 3 mm), actual wish to conceive who were scheduled for laparoscopic niche resection. Pre- and three months post-operatively, a vaginal swab was collected during the mid-luteal phase (cycle day 19 to 24). The microbiota composition was determined using 16S rDNA sequencing. Microbiota profiles were assigned to community state types (CST) based on the dominant bacterial species. Results: In total, 55 women completed sequential sampling. In all women, laparoscopic niche resection significantly reduced niche volume, with mean paired difference of 1766.6 mm3 (95 % CI: 640.4 – 2892.8). CST-IV was the dominant type both pre- and post-operatively (38.2 % vs 36.4 %, respectively). In ten (18.2 %) women the dominant CST changed after surgery. Three (5.5 %) women experienced a favourable change linked to fertility, while two (3.6 %) had unfavourable change and five (9.1 %) showed neutral shift. Women with favourable change had a greater reduction in niche volume (median reduction 1067.4 mm3 (p = 0.014)). Within a year, 23 (54.8 %) women became pregnant. The highest pregnancy rate (90.0 %, n = 9) was observed in women with post-operative CST-I, while the lowest rate (38.5 %, n = 5) was seen in those with CST-III. Conclusion: Laparoscopic niche resection resulted in a more than 10-fold reduction in niche volume. However, no significant changes in vaginal microbiota were observed postoperatively. Notably, women who experienced the largest reduction in niche volume also demonstrated a favourable shift in their microbiome profile, which is associated with improved fertility.Postoperatively, the highest pregnancy rate (90 %) was observed in women with Lactobacillus crispatus-dominant microbiota (p = 0.78). These results provide valuable insights into the pathophysiology of uterine niches and suggest potential therapeutic approaches for women experiencing niche-related infertility, however lager studies are needed to confirm these findings.