Hum. Reprod. Advance Access originally published online on July 18, 2007
Human Reproduction 2007 22(9):2575-2576; doi:10.1093/humrep/dem231
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Letters to the Editor |
Single embryo transfer in preimplantation genetic diagnosis cycles for women <36 years does not reduce delivery rate
Assisted Conception Unit and PGD Centre, Guy's and St Thomas' Hospital NHS Foundation Trust, London, UK
1 Correspondence address. Tel: +44-2071880496; Fax: +44-2071880490; E-mail: tarekeltoukhy{at}hotmail.com
We read with interest the paper by Donoso et al. (2007)
, and feel it is important to make the following comments.
The authors have attempted to assess the effect of a single-embryo transfer (SET) policy on delivery rate in young preimplantation genetic diagnosis (PGD) patients compared with a double-embryo transfer (DET) policy in a matched group of patients. They have concluded that there was no significant difference in the delivery rate between the two groups and supported the implementation of a SET policy in young women undergoing PGD.
We believe that this conclusion is somewhat flawed as it cannot be substantiated by the data presented by the authors for the following reasons.
First, the sample size (62 versus 73 embryo transfers) may not allow for assessing, with confidence, the statistical significance of the difference between the study and the control groups as the likelihood of a type II (
) error is high. For example, in order to detect a 10% difference (between 30 and 20%) in the delivery rate with 80% power at an alpha of 5%, we need 
230 embryo transfers in each group.
It is interesting to note that when the authors reported the outcome of SET and DET in the IVF/ICSI cycles without PGD during the same period (which presumably involved much larger numbers), DET was associated with a significantly higher delivery rate (a difference of 11.1% in the delivery rate per embryo transfer, P= 0.02). However, when they restricted the analysis to embryo transfers in cases treated with PGD due to the presence of Robertsonian and reciprocal translocations, a similar difference of 10.6% in the delivery rate per embryo transfer between the DET and SET groups was described as non-significant (P = 0.7). An even larger difference of 15.3% in the delivery rate per embryo transfer between patients who had an ‘elective’ SET (n = 27) and those who had a ‘non-elective’ SET (n = 46) was also described as non-significant.
Second, the historical control group used to study the difference in delivery rate per embryo transfer makes the assessment subject to bias.
Finally, the study results do not justify the study's own conclusion to support the implementation of an SET policy in young women undergoing PGD, simply because the majority of patients in the SET group (63.1%) had the SET imposed on them by the lack of more than one embryo available for transfer, rather than by the SET policy implemented in July 2003.
We believe in the merits of SET for the appropriate patients, but this enthusiasm on SET should not justify relaxing the methodological rigour with which those merits are scientifically judged. The authors rightly suggested that the lower pregnancy rate, technical complexity and high cost of PGD together with the reduced survival rate of cryo-thawed biopsied embryos must be considered. It is therefore all too important that the message we impart to our PGD patients must also be based on robust evidence.
Reference
Donoso P, Verpoest W, Papanikolaou EG, Liebaers I, Fatemi HM, Sermon K, Staessen C, Van der Elst J, Devroey P. Single-embryo transfer in preimplantation genetic diagnosis cycles for women <36 years does not reduce delivery rate. Hum Reprod (2007) 22:1021–1025.
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