The author concluded that there is insufficient evidence to suggest that the fluid-only method of embryo catheter loading is superior to the use of air brackets for increasing the odds of live birth, ongoing pregnancy or clinical pregnancy. Despite some limitations of the review, the author’s conclusion reflects the limited evidence.

To assess the efficacy of air fluid versus fluid-only models of embryo catheter loading techniques.

MEDLINE (via PubMed) (1966 to July 2006), EMBASE (1980 to 2006), the Cochrane CENTRAL Register (Issue 3, 2006), the National Research Register and Current Controlled Trials were searched. Additional studies were sought in reference lists of relevant primary studies, review articles and other relevant publications, and abstracts of major scientific meetings. Experts in the field and commercial companies were contacted for ongoing and unpublished trials. Studies in any language were included.

Study designs of evaluations included in the review

Randomised controlled trials (RCTs) were eligible for inclusion.

Specific interventions included in the review

Studies that compared embryo transfer through the cervical route using air brackets (e.g. air-fluid) versus the fluid-only method of embryo catheter loading were eligible for inclusion. Loading descriptions were reported.

Participants included in the review

Studies of women undergoing embryo transfer following in vitro fertilisation or intracytoplasmic sperm injection were eligible for inclusion.

Outcomes assessed in the review

Studies that reported live birth, ongoing pregnancy or clinical pregnancy rates were eligible for inclusion. The secondary outcomes were rates of embryo implantation, multiple and ectopic pregnancies, and miscarriage rates. Another outcome of interest was the presence of retained embryos in the tips of post-transfer catheters.

How were decisions on the relevance of primary studies made?

The author did not state how many reviewers selected the studies. [A: One reviewer selected the studies.]

The author reported on randomisation and allocation concealment methods. The author did not state how many reviewers performed the validity assessment. [A: One reviewer assessed validity.]

Where possible, data were extracted, using a standardised form, to enable intention-to-treat analysis. Where data were missing, authors were contacted for additional information. The author did not state how many reviewers performed the data extraction. [A: One reviewer extracted the data.]

How were the studies combined?

The pooled odds ratios (ORs) and corresponding 95% confidence interval (CIs) were calculated using a Mantel-Haenszel fixed-effect meta-analysis.

How were differences between studies investigated?

Statistical heterogeneity was assessed by visual inspection of the meta-analysis, and by using the chi-squared test.

Two RCTs (n=298) were included.

One of the two studies had a clearly reported randomisation procedure with adequate allocation concealment.

There was no significant difference between air fluid and fluid-only models of embryo catheter loading for live birth rate (1 study; OR 1.34, 95% CI: 0.59, 3.07), ongoing pregnancy rate (1 study; OR 1.34, 95% CI: 0.59, 3.07), clinical pregnancy rate (2 studies; OR 1.13, 95% CI: 0.70, 1.83), rate of embryo implantation (2 studies; OR 1.40, 95% CI: 0.77, 2.55), multiple pregnancy (1 study; OR 2.44, 95% CI: 0.09, 63.75), ectopic pregnancy (2 studies; OR 0.14, 95% CI: 0.01, 2.72), miscarriage (1 study; OR 1.18, 95% CI: 0.17, 8.02) and retained embryos (1 study; OR 0.96, 95% CI: 0.06, 15.79).

There is insufficient evidence to suggest that the fluid-only method of embryo transfer is superior to the use of air brackets.

The inclusion criteria were clear. The search was well conducted and the author took steps to minimise language and publication biases. The validity assessment was limited and measures to reduce reviewer error and bias were not employed in the review process. Details of the included studies were described in the text. Heterogeneity was assessed, and it appears that the studies were appropriately combined in a meta-analysis. Despite some limitations of the review, the author’s conclusion reflects the limited evidence.

Practice: The author did not state any implications for practice.

Research: The author stated the need for well-designed and powered RCTs to evaluate air fluid versus fluid-only models of embryo catheter loading.

Not stated.

This is a critical abstract of a systematic review that meets the criteria for inclusion on DARE. Each critical abstract contains a brief summary of the review methods, results and conclusions followed by a detailed critical assessment on the reliability of the review and the conclusions drawn.