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As the practice of freezing and transferring 'surplus' embryos widens rapidly, concerns about whether the freezing process may interfere with the viability of the embryos are often raised by patients.
A new study highlights that miscarriage is less likely to occur after the transfer of fresh embryos compared with frozen-thawed embryos, and also that the age of the embryos at the time of freezing could influence the miscarriage rate.
The study appears in the December issue of Reproductive BioMedicine Online.
Y.A. Wang and colleagues undertook a retrospective analysis of 52,874 clinical pregnancies recorded on the Australian and New Zealand Assisted Reproduction Database (ANZARD) between 2004 and 2008. The analysis showed that the woman's age and obstetric history are closely related to the risk of miscarriage, but that the transfer of fresh embryos is associated with fewer miscarriages than transfer of frozenthawed embryos.
The overall miscarriage rate was 18.7%. Younger women (less than 35 years) being almost 3 times less likely to miscarry than women over 40 years of age, and women who had an elective single embryo transfer were less likely to miscarry than if two embryos were transferred.
Transferring thawed embryos which were frozen at an earlier stage of development than the blastocyst were less likely to miscarry. The authors proposed transferring fresh blastocysts and freezing cleavage-stage embryos to reduce the miscarriage rate with IVF and related treatments.
They believe such a practice could lead to a substantial reduction in the miscarriage rate and eliminate much of the anxiety suffered by women undergoing Assisted Reproductive Technology (ART).
As noted by Yacoub Khalaf, Director of the Assisted Conception Unit at Guy's and St Thomas' NHS Foundation Trust, London, in a commentary in the same issue of Reproductive BioMedicine Online, this model for a new practice in ART may have practical limitations and would need to be validated through a randomized trial.
Large databases already collected over past years are rarely free of bias, nor are they comprehensive enough to account for all pertinent variables. Evaluation of this hypotheses in broad randomized trials is necessary for objective validation.
"It is interesting that miscarriage rates of frozen blastocysts were higher in the Australian study, particularly since it is well known that blastocysts have a lower frequency of chromosomal anomalies than cleaved embryos. Blastocyst culture is still a relatively new approach and culture-related factors such as selection for freezing at blastocyst stage may have affected early learning experiences in some clinics. It is therefore important to repeat a similar analysis of Australian clinic data during subsequent years," Dr. Jacques Cohen, senior editor of Reproductive BioMedicine Online, said of the study.
The article is "Transfers of fresh blastocysts and blastocysts cultured from thawed cleavage embryos are associated with fewer miscarriages" by Yueping Alex Wang, Michael Costello, Michael Chapman, Deborah Black, Elizabeth Anne Sullivan (doi:10.1016/j.rbmo.2011.07.023). The article appears in Reproductive BioMedicine Online, Volume 23, Issue 6 (December, 2011), published by Elsevier.
The commentary is "The search for a practice model to reduce miscarriage after assisted reproduction" by Yakoub Khalaf, Tarek El-Toukhy (doi:10.1016/j.rbmo.2011.09.014). The commentary appears in Reproductive BioMedicine Online, Volume 23, Issue 6 (December, 2011), published by Elsevier.
Full text of the article is available to credentialed journalists upon request; contact Greyling Peoples at 31-20-485-3323 or firstname.lastname@example.org. Journalists wishing to interview the authors may contact Alex Wang at email@example.com.
Reproductive BioMedicine Online was founded by Bob Edwards, the winner of the 2010 Nobel Prize in Physiology or Medicine. It covers the formation, growth and differentiation of the human embryo. It is intended to bring to public attention new research on biological and clinical research on human reproduction and the human embryo including relevant studies on animals.
Elsevier is a world-leading provider of scientific, technical and medical information products and services. The company works in partnership with the global science and health communities to publish more than 2,000 journals, including The Lancet and Cell, and close to 20,000 book titles, including major reference works from Mosby and Saunders.
Original article: http://www.eurekalert.org/pub_releases/2012-01/e-npm010512.php