What is the best site for embryo deposition? A systematic review and meta-analysis using direct and adjusted indirect comparisons

The site of embryo replacement has been postulated as being important to the success of IVF/ICSI. In order to determine the best site for embryo deposition during embryo transfer, a meta-analysis of randomized trials comparing different uterine deposition sites was undertaken. Electronic (e.g. PubMed, EMBASE, Cochrane Library, LILACS) and hand searches were performed to locate trials. Outcomes measures were the live-birth (LBR), ongoing pregnancy (OPR), and clinical pregnancy rates (CPR). Assessments of the endometrial cavity length (ECL) and the distance from the fundus to the tip of the catheter (DTC) were utilized. Six studies were identified, of which three were excluded. Meta-analysis was conducted with the Mantel-Haenszel method, utilizing the fixed-effects model. The LBR and OPR showed an increasing trend when transfers were performed to the lower half of the uterine cavity. For the DTC, all rates were significantly higher for the similar to 20 mm versus similar to 10 mm distance from the uterine fundus, supporting the results of the ECL analysis. The results of this systematic review show that there is limited evidence of the superiority of lower cavity transfers (e.g. similar to 20 mm) compared with the traditional high cavity (e.g. similar to 10 mm) transfers. More well-designed and powered randomized trials are needed to confirm this conclusion.