Pregnancy outcome after blastocyst transfer as compared to early cleavage stage embryo transfer

M. Montag1 and H. van der Ven

Department of Gynecological Endocrinology & Reproductive Medicine, University Clinics Bonn, Sigmund-Freud-Strasse 25, D-53105 Bonn, Germany

1 To whom correspondence should be adressed. Email: m.montag{at}uni-bonn.de

Sir,

We have read with great interest the retrospective cohort study on the possible benefit of blastocyst transfer (BS group) compared to cleavage stage transfer (CS group) on day 2–3 by Schwärzler et al. (2004)Go.

Based on their data, the authors conclude that blastocyst transfer may lead to a higher pregnancy rate with an overall better take-home baby rate at the cost of higher rates of multiples and preterm deliveries compared to cleavage stage transfer.

In order to enable the distinguished scientific community to appreciate as well as to discuss the authors' conclusions, we think that important data are missing in this article and should be made available.

Unfortunately, the authors do not give the details for the overall patient cohort. The statement in Material and methods regarding the study population only refers to those patients who were treated successfully and data are given in Table II. For this subgroup of patients the authors state that the CS group included patients classified as poor responders and patients who did not agree with a day 5 protocol. The main point here is, that poor responders present with low numbers of oocytes and consequently fewer embryos available for culture. It has been shown that poor responders have lower implantation and pregnancy rates compared to a control group (Ulug et al., 2003Go). It is also known that the pregnancy as well as implantation rates are poor if only those cleavage stage embryos can be transferred which are present, or in other words, if no further selection is possible (Devreker et al., 1999Go). It seems logical from this point of view that a probably biased CS group shows lower implantation rates as well as lower rates of multiple gestations, compared to the BS group.

Another major point is the mean age of the mother given for the subgroups of those patients who were treated successfully. The mean age in the CS group was 34 and in the BS group 31 years. Although the difference in age is not significantly different, the outcome of ART treatment is strongly dependent on age, especially in regard to a lower implantation rate and a higher aneuploidy rate in older patients. In combination with the arguments listed above, this could to some extent explain the superior performance of the BS group, especially in regard to the higher rate of multiples.

Most of the basic data are given in Table I. However, as previously mentioned, the study population which was the base for Table I is not described in the manuscript. Dependent on the number of low responders in the CS group, the results obtained could be biased by the patient selection.

Therefore, it would be beneficial to characterize the general study group and to present for both groups the raw data of the number of oocytes retrieved and the number of fertilized oocytes available for embryo culture and embryo selection in order to prove that the higher pregnancy rates are not an effect of a bias.

Because more and more infertility patients have a certain background of information derived from the internet, it is important for the consulting physician to give them a proper background information in order to help to find the treatment option which gives them the greatest benefit. In view of this, the article by Schwärzler et al. should be supplemented by those details, which are relevant in order to come to a profound, unbiased conclusion.

References

Devreker F, Pogonici E, de Maertelaer V, Revelard P, Van den Bergh M and Englert Y (1999) Selection of good embryos for transfer depends on embryo cohort size: implications for the ‘mild ovarian stimulation’ debate. Hum Reprod 14, 3002–3008.[Abstract/Free Full Text]

Schwärzler P, Zech H, Auer M, Pfau K, Göbel G, Vanderzwalmen P and Zech N (2004) Pregnancy outcome after blastocyst transfer as compared to early cleavage stage transfer. Hum Reprod 19, 2097–2102.[Abstract/Free Full Text]

Ulug U, Ben-Shlomo I, Turan E, Erden HF, Akman MA and Bahceci M (2003) Conception rates following assisted reproduction in poor responder patients: a retrospective study in 300 consecutive cycles. Reprod Biomed Online 6, 439–443.[Medline]





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