Prospective randomized study on day of embryo transfer

Byron Asimakopoulos1, Nikos Nikolettos1 and Safaa Al-Hasani2,3

1 Laborarory of Physiology, Faculty of Medicine,Democritus University of Thrace, Dragana, 68100 Alexandroupolis, Greece and 2 Department of Obstetrics/Gynecology,Medical University Lübeck, Ratzeburger Allee 160, D-23538 Lubeck, Germany

3 To whom correspondence should be addressed. e-mail: sf_alhasani{at}hotmail.com

Dear Sir,

We read the article of Van der Auwera et al. (2002) with great interest and we would like to congratulate the authors for this nice prospective randomized study. However, we would like to underline some points that may have caused bias in the conclusion.

Firstly, the numbers in Table II raise questions on the equal response to ovarian hyperstimulation between the two studied groups: there are 12.7% more retrieved oocytes, 14.99% more mature oocytes and 22.97% more fertilized oocytes in the day 5 group than the day 2 group. Therefore, these differences allow us to hypothesize that the two groups were not fully comparable. We were surprised that these differences were not found statistically significant by the authors.

Secondly, in the day 2 group, up to five fertilized oocytes were cultured per cycle and the rest were frozen. This fact reduced the chance for the selection of good embryos for transfer. On the contrary, in the day 5 group, all fertilized oocytes were cultured, so the selection was better. In Table IV, it is clearly demonstrated that there were 237 2 pronuclear (PN) oocytes available for culture in the day 2 group, while there were 415 2PN oocytes in the day 5 group (75.1% more). It is not clear whether the authors performed a statistical comparison between the two groups regarding the numbers of 2PN cultured oocytes. But it is certain that this difference influenced all the outcome variables.

Thirdly, the authors put emphasis on the clinical pregnancy per transfer and the implantation rate per transfer. We believe that these two variables should not be the main ones since a considerable number of cycles in the day 5 group had no transfer at all. On the other hand, the clinical pregnancy rate per oocyte retrieval (although influenced by the reduced number of 2PN oocytes in the day 2 group) showed no statistically significant difference between the two groups.

Finally, we would like to raise a question regarding the culture media. The Materials and methods section states that two different sequential media were used. Was there any effect on outcome? Was there any difference between the two groups according to the media used?

Apart from the above comments, we believe that Van der Auwera et al. (2002) presented an interesting prospective randomized study that is undoubtedly a very useful contribution to the discussion about the advantages of blastocyst culture.

References

Van der Auwera, I., Debrock, S., Spiessens, C., Afschrift, H., Bakelants, E., Meuleman, C., Meeuwis, L. and D’Hooghe, T.M. (2002). A prospective randomized study: day 2 versus day 5 embryo transfer. Hum. Reprod., 17, 1507–1512.





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