Choosing the Number of Embryos to Transfer

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The number of embryos transferred to your uterus will have a signficant impact on your chances of conceiving. It is clear that the greater the number of embryos transferred, the greater the chance of a pregnancy. Unfortunately, the greater the number of embryos the greater the risk of multiple pregnancy, and when a large number are transferred there may be a substantial risk of high-order (triplet or greater) multiple pregnancy. How then do we determine the number to place back? The answer depends upon many factors, including the stage of embryo development, whether the embryos are fresh or thawed, the age of the patient, the reason for IVF, the appearance of the embryos, results of prior IVF attempts, and the acceptability of selective embryo reduction. The American Society of Reproductive Medicine has provided recommendations for transfer numbers (PDF file), but they are merely guidelines. Note that they are designed to produce a reasonable pregnancy rate with a minimal multiple pregnancy rate, without considering embryo reduction.

In general, when fresh embryos are transferred on day 5 or 6 (blastocyst stage) it is advisable to transfer two. However, more may be replaced for older patients, prior IVF failures, or poor-looking blasocysts. Frozen-thawed blastocysts have about half the success rate of fresh, so we generally advise transferring 3 or 4, if available.  Again, however, this number may be upgraded due to other factors.

Day 3 embryos are more problematic, and while low numbers are recommended for young patients with excellent-looking embryos, there are many factors that might cause us to recommend transferring 3, 4, or even more embryos in some circumstances. As with blastocysts, thawed embryos are less likely to achieve pregnancy and usually require greater numbers for similar success.

The final decision as to the number of embryos to transfer is yours. Please read and consider this information, and discuss it with each other and your doctor. You will be asked to make a final determination on the day of your embryo transfer.

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