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How many Embryos to Transfer?
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Now that we have made it through the initial hurdles of IVF, we must now decide on when and how many embryos to transfer. The decision whether to perform a traditional Day 3 embryo transfer versus Day 5 blastocyst transfer is based on several factors, but mainly on the number and quality of embryos. The rule of thumb is that if the embryologist is unable to select the best two to three embryos of the bunch by Day 3, then growing the embryos to Day 5 will better differentiate those embryos (blastocysts) that have the best potential for implantation into the uterus. Embryos transferred at the blastocyst stage have made it through key growth processes and typically offer a greater chance of implanting. In addition, the blastocyst is given three distinct letter grades (A-F) based on the appearance of the inner cell mass (future fetus), trophoblast (future placenta), and cavity, whereas the Day 3 embryo is judged based on the number of cells present and overall appearance. Without compromising pregnancy rates, we need only return 1 or 2 blastocysts to the mother instead of the typical 2 or 3 early Day 3 embryos. In addition, the fewer embryos transferred the more may be available for cryopreservation for future use.
In general, older patients and poor responders with low numbers of eggs retrieved have a higher likelihood of ending up with a Day 3 transfer based on overall egg quality and subsequent embryo quality. In general, Day 3 transfers are limited to maximum of 3 embryos being transferred whereas Day 5 blastocyst transfers are limited to a maximum of 2 blastocysts being transferred. A significant benefit of blastocyst culture and transfer is the reduction of multiple births that can result from in vitro fertilization. This means that the many obstetrical complications that may arise from multiple pregnancies can be minimized. It is especially important in helping patients avoid having to make the difficult personal and ethical decisions regarding selective reduction.
Single Embryo Transfer
At Advanced Fertility Care, our goal is to provide a couple with a single healthy child. One of the negative side effects of IVF is that of multiple pregnancies. Our own success data shows that at AFC, we are very successful at achieving pregnancies. In general, when two to three embryos are transferred, we have seen a twin pregnancy rate of approximately 40%. In addition, our own internal data has also shown that for women under age 35 who have multiple high quality blastocysts on Day 5, the implantation rate is well above 90% in our Center. This can be interpreted to mean that for those patients who have multiple high quality blastocysts on Day 5, they will be pregnant with however many blastocysts are transferred. It is for this patient population that we highly recommend a single blastocyst transfer. By limiting the transfer to a single blastocyst, the overall success rate is only minimally decreased (less than 6%), while the risk of multiple pregnancy is reduced from 40% to 3-4% (the chance of one embryo splitting on its own after transfer). There are also certain circumstances such as congenital uterine anomalies, small maternal pelvis, or previous pregnancy complications that may mandate a singleton pregnancy in order to lower the risk for adverse effects on the mother.
Regardless of the circumstances, Dr. Zoneraich and our embryology staff will discuss the specifics of your case with you on the day of transfer and provide you with our expert recommendations as to the number of embryos that we recommend for transfer. The decision is ultimately yours as to the number of medically appropriate embryos that will be transferred.
