A large retrospective study has yielded information on the optimal number of blastocyst stage embryos to transfer on day 5 or 6 in women aged 38 years or older.
Specialists in a Writing Group convened by the USA’s Society for Assisted Reproductive Technology conducted the study, based on data collected by the society between 2000 and 2004. The data related to a total of 5,569 day 5 and day 6 embryo transfers in women aged 38 or older who were undergoing their first assisted reproductive technology cycle. These 5,569 transfers led to 1,667 deliveries.
The researchers used both univariate and multivariate logistic regression to model the probability of delivery, twins, and higher-order multiples based on certain patient characteristics. These were age, the number of embryos transferred, the maximum follicular phase FSH level, the number of oocytes retrieved, cryopreservation of excess embryos, and the use of ICSI.
In their new paper in the current issue of the journal Fertility and Sterility, the researchers report the findings of their analyses. In women aged 38 or 39 years, there was an increase in delivery rates when two embryos were transferred, compared with when one embryo was transferred. Transferring more than two increased the rate of multiples but not delivery.
In women aged 40 years, transferring up to three embryos increased the delivery rate without increasing the multiple rate. In women aged 41 or 42 years, the delivery rate plateaued after the transfer of three embryos, but the twin rate continued to increase.
In the paper, the researchers draw their findings together in order to present the following recommendations on the suggested number of embryos to transfer on days 5 and 6 to minimize the risk of multiples in patients undergoing their first cycle:
Number of oocytes <10 and no cryopreservation:
Maternal age 38 years: 2 embryos.
39 years: 2.
40 years: 2-3.
41-42 years: 3.
43-44 years: 3.
Number of oocytes 10 or more, and/or use of cryopreservation:
Maternal age 38 years: 1-2 embryos.
39 years: 1-2.
40 years: 2.
41-42 years: 2-3.
43-44 years: 3.
Discussing their findings, the researchers note that these recommendations of course “do not represent strict guidelines” but do represent an analysis of outcomes from a large national US dataset. They write: “From this analysis, it appears that, in patients aged 38 to 39 years who are considered candidates for blastocyst transfer, delivery rates can be maximized while minimizing multiple pregnancy rates by transfer of no more than two blastocyst stage embryos.”
The researchers acknowledge that different laboratories can have significantly different stimulation protocols, indications for blastocyst stage transfer, and classifications of embryo morphology, and point out that these differences were not taken into account in the data analyzed and presented.
Source: Fertility and Sterility 2009;91:157-66
