Embryo transfer preparation techniques not supported by evidence

Routine preparation techniques used before embryo transfer may not improve pregnancy rates, according to a Cochrane review.

Embryo transfer is the final stage of an IVF cycle, when doctors place an embryo into the uterus using a catheter passed through the cervix. Several preparation techniques are used to aid the transfer, but a new Cochrane review found no clear evidence that they improve pregnancy rates.

'To an extent, this is a case of tradition driving practice rather than the evidence,' said the report's co-author Dr Ryosuke Akino, an obstetrician-gynaecologist from Kato Ladies Clinic in Tokyo, Japan. 'Current practices in this area often reflect local protocols, clinician preference, and historical convention rather than strong, high-quality evidence.'

The researchers assessed 11 studies involving 2524 women undergoing embryo transfer. They examined three approaches: having a full bladder, removing mucus from the cervix, and afterloading, where doctors position the catheter before loading the embryo. A full bladder can straighten the angle between the cervix and uterus, while removing cervical mucus may prevent it from blocking the catheter or interfering with embryo release.

However, the review found inconclusive evidence about whether these approaches improve pregnancy or live birth rates. The authors noted that the included studies were generally small and provided low-certainty evidence, meaning the researchers had limited confidence in the findings.

Dusko Ilic, professor of stem cell science at King's College London, who was not involved in the review, commented: 'Some measures, such as bladder filling or afterloading, may still make catheter placement easier in selected patients, even if a direct improvement in pregnancy rates has not been demonstrated. These findings support selective, clinically justified use rather than routine use based solely on tradition.'

The review also found that the techniques are generally considered safe and that the associated risks 'mostly relate to discomfort … rather than clinical harm'. However, adverse events were not reported in the studies, and could not be evaluated. A previous review from the Cochrane group, published in 2009, reached similar conclusions.

Consultant gynaecologist Dr Sesh Sunkara from King's College London, who was not involved in the review, noted that 'there would be no … extra costs from the common practice of embryo transfer with full bladder or from the use of embryo afterloading.' In this respect, embryo transfer preparation techniques differ from so-called IVF 'add-ons' for which patients are charged extra.

The authors called for more research to clarify the role of these techniques in embryo transfer: 'These small changes and techniques have the possibility to make a massive difference, but we won't know more until more robust, better-quality trials are conducted,' said Dr Noyuri Yamaji of Showa Medical University in Tokyo who led the review.