No clear evidence common embryo transfer techniques improve IVF success, review finds

Common IVF preparation techniques used before embryo transfer have no proven effect on pregnancy rates, according to a review.

Researchers said evidence for the widely used practices remains uncertain because available studies are limited and generally of low quality.

Embryo transfer is the final and most vulnerable stage of IVF, when an embryo is placed into the womb. Only around one in three transfers results in pregnancy.

Practice varies between clinics, with some routinely using preparation techniques such as adjusting bladder fullness while others do not consider them necessary.

Dr Ryosuke Akino, practising obstetrician-gynaecologist from Kato Ladies Clinic, said: “To an extent, this is a case of tradition driving practice rather than the evidence.

“Current practices in this area often reflect local protocols, clinician preference, and historical convention rather than strong, high-quality evidence.”

The Cochrane review analysed 11 studies involving 2,524 women undergoing embryo transfer.

Researchers looked at three preparation techniques used by fertility clinics: having women arrive with a full bladder to straighten the angle between the uterus and cervix, removing cervical mucus and using a technique called afterloading.

Afterloading is a technique used to guide the embryo through the cervix.

The review found no reliable evidence that any of the three approaches improved pregnancy rates compared with standard care.

Researchers rated the evidence as low or very low certainty because the trials were small and had methodological weaknesses. They found no grounds to recommend any of the techniques over standard care.

There was also limited information about possible side effects.

The review team, which included methodologists and practising obstetrician-gynaecologists, said full bladder preparation and cervical mucus removal were generally considered safe, with no clear evidence of harm or major complications.

Dr James Brown, obstetrician-gynaecologist from Women’s Health and Research Institute Australia, said: “While these techniques are generally considered safe, it’s still important to test their effectiveness.”

Akino and Brown added: “A full bladder can be uncomfortable, although it may ease catheter insertion in certain uterine positions and reduce procedural difficulty.

“Mucus removal is usually quick, but if done roughly and causes bleeding, it may affect the woman’s experience.

“Overall, the risks are minor and relate mostly to discomfort and procedural factors rather than clinical harm.”

The authors said embryo transfer has changed relatively little despite major advances elsewhere in IVF.

Research has instead focused more heavily on embryo quality and genetic factors, which have a greater bearing on treatment success than transfer technique.

Embryo transfer also depends heavily on the person carrying out the procedure and can be difficult to standardise, making large, rigorous clinical trials harder to design.

Researchers said women may also be reluctant to risk valuable embryos by taking part in randomised studies comparing different transfer techniques.

Dr Noyuri Yamaji from Showa Medical University in Japan said: “Sixteen years of research still haven’t answered a basic IVF technique question.

“This is a critical step in the IVF process and 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.”

All the studies assessed were carried out in high-income countries, meaning the findings may not necessarily apply to other healthcare settings and populations.

The authors said further research could be particularly valuable in resource-limited settings, where these procedures are inexpensive and simple to change and basic procedural standardisation could matter more than advanced technical modifications.