**6. Antimicrobials and ART**

Although the reproductive tract microbiome remains relatively poorly understood in terms of its relationship to reproductive outcomes, there is a long history of attempting to influence it with the use of prophylactic antibiotics at the time of procedures during ART. This has been a practice ingrained since 1978, when it was suggested that contamination during ART procedures could negatively affect outcomes [101]. Because antiseptics, such as povidone iodine, can have a negative impact on embryos, antibiotics were turned to as a way of manipulating the microbiome [102].

A common time for antimicrobial prophylaxis is at the time of ET. Given the concern for colonization of the transfer catheter tip with microbiota from the upper genital tract, antibiotics have been proposed as a way to decrease inoculation of the uterine cavity and thereby increase pregnancy rates. Despite this widespread practice, relatively little data exist to support or refute antibiotic use.

A recent Cochrane review analyzed randomized controlled trials in the literature that investigated antibiotics at ET [103]. Only four potential studies were identified, of which three were excluded. The remaining study reported on clinical pregnancy rates as the primary outcome. Although administration of antibiotics reduced microbial contamina‐ tion as defined by culture of ET catheter tips, the clinical pregnancy rate was 36% in those receiving antibiotics and 35.5% in those not receiving antibiotics (odds ratio 1.02, 95% confidence interval 0.66–1.58) [104]. The reviewers concluded that more evidence is needed with live birth as the primary outcome.
