Key messages
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Any benefits in terms of pregnancy chances of full bladder, removing mucus from the cervix, or afterloading (loading the embryo into the catheter after it has been placed in the uterus) are unclear, and information on unwanted effects was rarely reported.
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Further larger and well-designed studies are needed to improve our confidence in the evidence on the effects of preparation techniques before embryo transfer.
What is in vitro fertilisation and embryo transfer?
In vitro fertilisation (IVF) is a type of fertility treatment. An egg is fertilised by sperm in a laboratory, and the resulting embryo is placed in the uterus (womb) to develop as normal. The embryo is transferred through a tube (catheter) that is inserted into the vagina and through the neck of the womb (cervix) into the uterus. This is the last step in the IVF process and is the most likely to go wrong. Only one-third of transfers result in pregnancy.
Clinicians use various techniques to improve the success of embryo transfer. For example, inserting the catheter may be easier if the woman has a full bladder, or if doctors clear away any mucus from the cervix. The type of catheter used, positioning the catheter first and then putting the embryo in the catheter (called ‘afterloading’), or carrying out a practice procedure may also help.
What did we want to find out?
We wanted to find out the effects of preparation techniques before embryo transfer on live birth rate, unwanted effects, pregnancy rate, pregnancy loss rate, and difficulty of transfer.
What did we do?
We searched for studies comparing preparation techniques before embryo transfer with no special preparation techniques in women with infertility having IVF. We compared and summarised the results of the studies and rated our confidence in the evidence using structured methods and standard tools, based on factors such as study methods and sizes.
What did we find?
We found 11 studies involving a total of 2524 women with infertility who were undergoing embryo transfer. The studies were conducted in Canada, the USA, Argentina, Brazil, Belgium, Greece, Italy, the Netherlands, Spain, the UK, Turkey, and Japan. Six of these studies looked at techniques including:
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adjusting bladder fullness;
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cleaning the mucus from the cervix; and
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afterloading.
Main results
Embryo transfer under a full bladder versus an empty bladder
We are very uncertain about the effect of a full bladder versus an empty bladder on pregnancy rate, pregnancy loss rate, and difficulty of transfer.
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Live birth rate: not reported
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Pregnancy rate (2 studies, 273 women)
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Pregnancy loss rate (1 study, 131 women)
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Difficulty of transfer (1 study, 142 women)
Removing mucus versus no mucus removal
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Live birth rate: one study reported 52 live births per 220 cycles in the mucus removal group and 42 live births per 205 cycles in the no-mucus removal group.
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Pregnancy rate: there may be little to no difference between groups in pregnancy rate (1 study, 97 women). A second study reported 65 pregnancies per 220 cycles in the mucus removal group and 63 pregnancies per 205 cycles in the no-mucus removal group.
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Pregnancy loss rate: one study reported 15/220 cycles in the mucus removal group and 20/205 cycles in the no-mucus removal group.
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Difficulty of transfer: not reported
Embryo afterloading versus direct embryo transfer
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Live birth rate: not reported
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Pregnancy rate: there may be little to no difference between groups in pregnancy rate (2 studies, 654 women).
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Pregnancy loss rate: there may be little to no difference between groups in pregnancy loss rate (1 study, 352 women).
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Difficulty of transfer: we are very uncertain about the effect of embryo afterloading versus direct embryo transfer on difficulty of transfer: one study reported that afterloading may reduce the difficulty of transfer (352 women), while a second study reported there was no difficulty of transfer for both groups.
What are the limitations of the evidence?
We have little to very low confidence in the evidence. The available research is limited, and most studies were small in size and old. This means we cannot be sure which, if any, of these individual preparation techniques (e.g. full bladder, mucus removal, afterloading) are effective or safe, so the findings should be interpreted with caution. More high-quality research is needed to find out whether any of these preparation techniques truly improve IVF outcomes and to better understand their possible unwanted effects.
How up to date is this evidence?
This review is an update of our previous review published in 2009, with literature searches conducted up to October 2025.
Vollständige Zusammenfassung lesen
Embryo transfer (ET) is the final and most vulnerable step in in vitro fertilisation (IVF) treatment. Pregnancy rates after ET may be influenced by several factors including cervical preparation, the performance of a dummy or mock transfer, the choice of catheter, the use of ultrasound guidance, removing the mucus or blood on the catheter, and straightening of the utero-cervical angle. Recent research has focused on improving the embryo transfer technique in the hope of increasing the success rates of IVF. This review focused on preparation techniques as it is unclear whether these simple interventions will make ET an easier procedure with higher success rates and lower complication rates.
Zielsetzungen
To assess the benefits and harms of different preparation techniques prior to ET.
Suchstrategie
We searched the Cochrane Gynaecology and Fertility Group's Specialised Register, CENTRAL, MEDLINE, Embase, and PsycINFO on 6 October 2025. We handsearched the citation lists of relevant publications, reviews, and included studies. We contacted experts in the field and searched trial registries to identify any unpublished or additional trials.
Auswahlkriterien
Only truly randomised controlled trials of the interventions straightening the utero-cervical angle, dummy transfer prior to ET, cervical and endometrial preparation, and embryo afterloading were included. The primary outcomes were live birth rate and pregnancy rate per woman randomised. Participants were women with any type of subfertility undergoing IVF treatment and reaching the ET stage.
Datensammlung und ‐analyse
Two review authors critically appraised potentially eligible studies. Ten studies were included in this review and data were independently extracted by two review authors. Disagreements were resolved by discussion and involvement of a third author. Risk of bias was also independently assessed by two authors. Dichotomous outcome data were expressed as Peto odds ratios. Subgroup analysis and the investigation of heterogeneity were planned.
Hauptergebnisse
At the time of ET, there was no evidence of benefit with the following interventions: full bladder, removal of cervical mucus, flushing the endocervical canal or the endometrial cavity. We did not identify any eligible studies for dummy transfer, changing patient position, the use of a tenaculum, or embryo afterloading.
Schlussfolgerungen der Autoren
We added three new studies in this update, but their inclusion did not change the main conclusions of the review. No specific implications for practice are made based on the available evidence. There is a need for further and larger studies on ET preparation techniques, which should be better designed, with clearly described methods and inclusion and exclusion criteria, and greater numbers of participants.
Finanzierung
This Cochrane review had no dedicated funding.
Registrierung
Protocol and previous versions available via https://doi.org/10.1002/14651858.CD007682, and https://doi.org/10.1002/14651858.CD007682.pub2.
