Human Reproduction, Vol. 18, No. 4, 893,
April 2003
© 2003 European Society of Human Reproduction and Embryology
Prospective randomized study on day of embryo transfer
Leuven University Fertility Center, UZ Gasthuisberg, Leuven, Belgium
1 To whom correspondence should be addressed. e-mail: thomas.dhooghe{at}uz.kuleuven.ac.be
Dear Sir,
We thank Dr Asimakopoulos and Dr Al-Hasani for their efforts to critically address several issues regarding our study (Van der Auwera et al., 2002
).
Firstly, their presumption that there were significant differences between the day 2 group and the day 5 group regarding oocytes, mature oocytes and fertilized oocytes is not true. It can easily be calculated from Table II that there are no differences between the day 2 group and the day 5 group in the mean number of oocytes/patient (10.7 and 11.5), the proportion of mature oocytes/total number of oocytes (84 and 86%) or the percentage of fertilized oocytes/total number of mature oocytes (61 and 65%).
Secondly, we acknowledged in our Discussion that an important weakness was introduced in the study by freezing supernumerary pronucleate ova in group 1 if patients had more than five fertilized oocytes, as has been commented by Dr Asimakopoulos and Dr Al-Hasani. Even then, the implantation rate per embryo was 39% on day 2 if more than five pronucleate ova were available, suggesting that this bias was limited in nature, i.e. this implantation rate per embryo on day 2 is still among the highest reported in the literature.
Thirdly, we disagree with Dr Asimakopoulos and Dr Al-Hasani that we only put emphasis on the clinical pregnancy rate or implantation rate per embryo transfer and not on per oocyte retrieval. In the Abstract, in Table III, Table VIIa and Table VIIb, and in the Discussion we discuss this issue at great length, including the importance of cryo-augmented pregnancy rate per oocyte retrieval. Indeed, we clearly mentioned that the cryo-augmented delivery rate per oocyte retrieval was not significantly higher in the blastocyst embryo transfer group 2 (36.3%) than in the day 2 embryo transfer group (28.6%). We also explained that we stopped this study prematurely due to the unexpectedly high percentage of twin deliveries (53 and 37.5% in the day 2 group and the blastocyst group respectively), as can be seen in Table III and in the Discussion.
Finally, it is correct that two different sequential media were used. The data regarding outcome in pregnancy rate and implantation rate on day 2 and day 5 will be published in a separate paper.
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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