How Many Embryos

How Many Embryos Should I Transfer Back?

3 blastocysts

This question is one of the most frequently asked of RE’s and for completely understandable reasons. Unfortunately, this issue is usually only addressed with the patient in the transfer room, with a full bladder, therefore somewhat unable to concentrate properly. The doctor is usually rushed and behind schedule due to a difficult transfer just completed. All things considered, this issue cannot be satisfactorily addressed in this fashion.It has been known since the early days of IVF, that success rates for pregnancy initiation, increased with higher numbers of embryos transferred. Generally speaking however, the pregnancy initiation rate only increased up to 4 embryos transferred, and then the rate of pregnancy reached a plateau. Beyond 4 embryos transferred, the multiple pregnancy rate is the only thing that changed. For the most part, multiple pregnancies are not a desired outcome as a result of IVF treatment.

There is a small group of patients who actually desire twins, but in over 20 years of clinical IVF, very few patients have requested triplets or more as the desired outcome. IVF practitioners have been concentrating on ways to decrease or ideally completely eliminate the incidence of multiple pregnancy from this work. Many are advocating what is called SET (single embryo transfer). Because of the pressures of expense and lack of insurance coverage for IVF services, practitioners are confronted with the dilemma and walking the tightrope between trying to initiate a pregnancy, while at the same time, minimizing or eliminating the risks of multiple pregnancy. Most certainly HOM (high order multiples – i.e. triplets or greater), should be avoided at all costs, because of the risks to both mother and children, in what can potentially become a lifetime of anguish, especially if there are significant deficits as a consequence of a preterm delivery.

However, until such a time as we are definitively able to identify those embryos in the lab, which are the most likely to implant (and there is abundant ongoing research in this area), practitioners and patients are still confronted with the issue of how to maximize the chance of conception, while at the same time minimizing the risks of multiple pregnancies. The discussion of methods to select embryos and embryo grading systems, are comprehensively addressed in other handouts and will not be repeated here. Please request these handouts if they have not already been provided.With this as the background information, the patient/couple, should have the following discussion before coming to the office for the embryo transfer and before that rushed conversation with the full bladder in a cold exam room, half naked. Issues to consider:

AGE of the person donating the eggs. Age of the recipient in an egg donor case.

Age of the person providing the eggs. The younger the person donating the eggs, the fewer embryos should be replaced. This is because we know that the younger the person, a greater percentage of the embryos, are likely to implant. Recent research has demonstrated that for patients aged 38 and 39 y.o. delivery rates increase up to 2 embryos transferred (i.e. DR for 2 embryos is > than for 1 embryo transferred) but beyond 2 embryos, only the multiple rate increased. For patients 40 years old, this difference occurred at 3 embryos. In egg donor cycles, the age of the recipient is somewhat important as the uterine perfusion will decrease with advancing age. In my practice I differentiate between recipients >48 and those < 48 years old. However, the risks of multiple are especially significant in oider gravidas.


How many prior failures of IVF have taken place

The more failed cycles a patient has had prior to the instant transfer, the greater is the tendency to transfer higher numbers of embryos. A word of caution however is that if the failures have been due to a previously undiagnosed issue (e.g. immune disorder), which has now been addressed and treated, consideration should be given to the fact that the prior failures were due to the lack of attention to the immune disorder.


Quality of the embryos

The quality of the embryos will greatly influence this decision. Recognizing that our ability to optimally select embryos is rather limited, and until such time as this improves, the general principle is that the older the patient, the more embryos can be replaced without concerns for HOM.


How was the cycle

If a cycle was poor i.e. suboptimal stimulation with low E2’s, then the resulting embryos are likely to be suboptimal and accordingly, a greater number of embryos can be safely transferred. However, there is a point at which if a cycle was so poor during the stimulation, one should question why the cycle was not canceled.


Would twins represent an acceptable outcome

Couples must know between themselves whether twins would be an acceptable outcome. If the answer is yes, one can afford to be more aggressive (within reason) in the number of embryos transferred.


What are the beliefs relating to selective pregnancy reduction.

Selective reduction is usually performed at 8-11 weeks of gestation (to allow the pregnancy to declare itself as a true multiple pregnancy). Some patients are ethically and morally opposed to this intervention. If that is the case, a higher degree of caution must be exercised in the decision as to the number to transfer. A frequent question asked is whether the procedure itself will cause significant risks to the surviving pregnancies. The answer is that the procedure MUST be performed by someone skilled in this procedure. There is a slight risk to the remaining embryos but it is lower than the risks posed by continuing the multiple pregnancy. Selective reduction is usually done for triplets or greater and is seldom done for twins.


Is the transfer being done on day 3 or day 5 (blastocyst)

By waiting for day 5 (occasionally day 6) i.e blastocyst transfer, there is a greater opportunity for the embryology staff to identify the embryo(s) most likely to implant and accordingly, the numbers of embryos transferred should be more conservative than less conservative. Remaining embryos are usually left in culture and are only frozen if they attain the blastocyst stage of development. Obviously the clinic must have a reputable freezing program.


Summary: With the above framework, the usual practice is to transfer either 2 or 3 embryos. We are not yet at the place where routine SET makes sense for most patients, although that is where we are headed.If you would like more specific information on this topic, specifically related to embryo grading systems, embryo selection techniques, PGD (pre-implantation genetic diagnosis), please request this and it shall be provided.