More information about embryo transfer days

Patients often ask us about the differences between embryo transfer days. We can do a transfer on Day 3 or Day 5.  Many of our patients are internet savvy. They seem to all want Day 5 transfers, as they believe that the “literature” says it’s best.  In fact, if you look at basic statistics, it does look like Day 5 results are better.

Why there are differences between embryo transfer days

There are several possible explanations for this.  First of all, it could be that longer incubation of embryos in the laboratory allow the better embryos to grow.  This would increase the likelihood that we transfer better quality embryos to the patient’s uterus.

Second, some people have suggested that longer incubation in the laboratory can actually “rejuvenate” poor quality embryos.  As a result, delaying the transfer could allow embryo quality to improve.

Third, it is possible that delaying the transfer to Day 5 allows for better synchrony between the embryo and the uterus. This could theoretically result in improved pregnancy rates.

Finally, it is possible that physicians advise patients with many good quality embryos to delay their transfer to Day 5.  By doing this, patients with the best prognosis for pregnancy are in the Day 5 group. This could be artificially raising the pregnancy results in this group.

Diving deeper into this topic

In science, and in clinical medical research, the best way to answer questions like these is to perform a prospective, randomized trial.  An investigator takes 100 patients and divide them at random into two treatment groups.  In this example, 50 would have an embryo transfer on Day 3. 50 would have a transfer on Day 5.  They would compare pregnancy and delivery rates to see if there is a statistical difference in outcome between the two treatments.

In fact, people have done this research in both America and Europe.  Most of these studies show there is no difference in pregnancy or delivery rates between Day 3 and Day 5 transfers.  In addition to well designed clinical trials, there is also a compilation of the literature – published by the Cochrane Collaboration – that shows no difference between these two treatments.

In summary, it appears from the medical literature that delaying embryo transfer to Day 5 offers no advantage to the typical patient undergoing IVF.  The numerically higher pregnancy rates observed in most programs with Day 5 transfers can most likely be explained by the fact that physicians advise patients with many high quality Day 3 embryos to delay their transfer. Contact us to learn more.