In vitro fertilisation (IVF) using single embryo transfer boosts success and safety, reported five newspaper articles on 21 February 2008 (1-5). The generally accurate reports were based on a large before- and after-study that found beneficial effects of a single embryo transfer strategy aimed at a selected group of women.
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Five newspaper articles reported that IVF by a new technique using single embryo transfer results in higher pregnancy rates and a reduction of multiple pregnancy rates (21 February 2008) (1-5).
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The reports were based on a study comparing two cohorts of patients treated under different embryo culture and transfer strategies published in the British Journal of Obstetricians and Gynaecologists, (6). The researchers investigated the impact of a single embryo transfer strategy in a selected group of women on clinical pregnancy rate and multiple pregnancy rate. Women with high risk of multiple pregnancy were offered an extended embryo culture and transfer of a single embryo that had reached the blastocyst-stage after 5 days of in vitro culture instead of transferring up to three embryos after 2-3 days. The authors found higher pregnancy rates and lower multiple pregnancies associated with the new transfer strategy.
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The newspaper reports on this study were generally accurate. Although the study design used by the authors demands that caution is needed when interpreting the findings, this study appears well conducted and the results are likely to be reliable.
Evaluation of the evidence base for selective single blastocyst transfer to reduce the multiple pregnancy rate and increase pregnancy rates
Where does the evidence come from?
The research was conducted by Dr. Yakoub Khalaf and colleagues based at the Assisted Conception Unit at Guy's and St. Thomas' Hospital NHS Foundation Trust London.
What were the authors' objectives?
The aim was to examine the clinical pregnancy rate and multiple pregnancy rate in a large IVF programme before and after introduction of a single embryo transfer strategy in a selected group of women.
What was the nature of the evidence?
This was a pre- and post-intervention study performed between July 2004 and June 2007 that compared two embryo culture and transfer strategies. It involved overall 2,451 IVF cycles performed at the Assisted Conception Unit at Guy's and St. Thomas' Hospital NHS Foundation Trust in London. The mean age of the women included in the study was 35.2 in the pre-intervention group and 35.8 in the post-intervention group.
What interventions were examined in the research?
Between July 2004 and December 2005 (pre-intervention period) the clinic employed a strategy where up to three cleavage-stage embryos were transferred to the uterus 2-3 days after fertilisation. From January 2006 to June 2007 a new strategy was implemented. Women were given audiovisual and written educational information on the risks of multiple pregnancy and advantages of single blastocyst transfer. A selected group of women with a good prognosis, who also had a high risk of multiple pregnancy, were offered single blastocyst transfer. This technique comprised extended embryo culture to allow further development of the embryo (until the blastocyst-stage was reached at day 5) and subsequent transfer of a single high-quality-blastocyst to the uterus instead of the usual two or three cleavage-stage embryos. The strategy of up to three cleavage-stage embryo transfer was still offered to women who did not meet the criteria for single blastocyst transfer. The eligibility criteria for the single blastocyst transfer were fulfilled by 19% of cycles reaching embryo transfer.
What were the findings?
The overall pregnancy rate per cycle started increased from 27 percent during the pre-intervention period to 32 percent in the post-intervention period when single-blastocyst transfer was offered to certain women with high risk of multiple pregnancy. At the same time, rates of multiple pregnancies per clinical pregnancy decreased from 32 percent to 17 percent. Both results were statistically significant.
What were the authors' conclusions?
Selective single blastocyst transfer in women with good prognosis can reduce the multiple pregnancy rate while maintaining the overall success rate of an IVF programme.
How reliable are the conclusions?
The authors compared two cohorts of patients to assess the impact of a single embryo transfer strategy. This study design was a pragmatic approach in the context of the research question but it is known as a rather weak evaluation design in terms of constructing confident causal knowledge. The crucial assumptions are that there are no selection differences between both groups at baseline and that all other factors which are likely to influence the outcome are fully known. The authors' conclusions about the effect of the introduction of the new embryo culture and transfer strategy on the clinical outcomes of the unit seem reasonable. However, it is important to bear in mind that the study was not designed to provide a reliable estimate of clinical outcomes with selective single blastocyst transfer compared to multiple cleavage-stage embryo transfer. Additionally, detailed information on the characteristics specifically of these women who were eligible to receive and who actually received single blastocyst transfers would have been desirable. Live birth rate was not reported so it is unclear what impact this new strategy had on the most important outcome for patients
Systematic reviews
Information staff at CRD searched for systematic reviews relevant to this topic. Systematic reviews are valuable sources of evidence as they locate, appraise and synthesize all available evidence on a particular topic.
There were two related systematic reviews identified on the Cochrane Database of Systematic Reviews (CDSR) (7,8) and one on the Database of Abstracts of Reviews of Effects (DARE) (9).
References and resources
1. One embryo at a time 'makes IVF less risky'. The Daily Telegraph, 21 February 2008, p8.
2. New IVF technique: greater success rate, fewer multiple births. The Independent, 21 February 2008, p8.
3. Fertility clinic boosts safety and success. The Guardian, 21 February 2008, p5.
4. Couples are warned over 'buy one, get one free IVF babies'. Daily Express, 21 February 2008, p31.
5. Using older embryos 'could boost IVF pregnancy rates'. The Daily Mail, 21 February 2008, p31.
6. Khalaf Y, El-Toukhy T, Coomarasamy A, Kamal A, Bolton V, Braude P. Selective single blastocyst transfer reduces the multiple pregnancy rate and increases pregnancy rates: a pre- and postintervention study. BJOG: An International Journal of Obstetrics and Gynaecology 2008;115(3):385-390.
7. Pandian Z, Bhattacharya S, Ozturk O, Serour GI, Templeton A. Number of embryos for transfer following in-vitro fertilisation or intra-cytoplasmic sperm injection. Cochrane Database of Systematic Reviews 2004, Issue 4. Art.No.: CD003416. DOI: 10.1002/14651858.CD003416.pub2.
8. Blake DA, Farquhar CM, Johnson N, Proctor M. Cleavage stage versus blastocyst stage embryo transfer in assisted conception. Cochrane Database of Systematic Reviews 2007, Issue 4. Art. No.: CD002118. DOI: 10.1002/14651858.CD002118.pub3.
12. Dare M R, Crowther C A, Dodd J M, Norman R J. Single or multiple embryo transfer following in vitro fertilisation for improved neonatal outcome: a systematic review of the literature. Australian and New Zealand Journal of Obstetrics and Gynaecology 2004;44(4):283-291. [DARE Abstract]
Consumer information
NHS Direct - IVF
British Fertility Society
Human Fertilisation and Embryology Authority
Further information about Hitting the Headlines
Further information about Hitting the Headlines, together with selected relevant links, can be found at http://www.library.nhs.uk/hth/.
