Air fluid versus fluid-only models of embryo catheter loading: a systematic review and meta-analysis

The objective of this systematic review was to determine the beneficial or detrimental effect of using air bubbles to bracket the embryo-containing medium during embryo transfer. To test this theory, a meta-analysis of randomized trials comparing air fluid versus fluid-only methods was performed. The primary outcome measures were live birth, ongoing and clinical pregnancy rates. The secondary outcome measures were the rates of implantation, miscarriage, multiple and ectopic pregnancies and retained embryos. Electronic (e.g. PubMed, EMBASE, Cochrane Library) and hand searches of the literature revealed two included studies (298 women). Meta-analysis was conducted using the Mantel–Haenszel method (fixed-effect model). For the primary outcome measures, there were no significant differences between the two methods with regards to live birth (OR = 1.34; 95% CI = 0.59–3.07), ongoing pregnancy (OR = 1.34; 95% CI = 0.59–3.07) and clinical pregnancy (OR = 1.13; 95% CI = 0.70–1.83) rates. For the secondary outcomes, there were no significant differences between the two groups. In conclusion there is insufficient evidence to suggest that the fluid-only method is superior to the use of air brackets during embryo loading. There is a need for well-designed and powered randomized trials to determine any possible benefit to either method.