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Blastocyst Transfer

Blastocysts are 5 or 6 day old embryos that have divided into enough cells to be ready to hatch out of their zona pellucidas. Blastocysts are generally more likely to grow into viable pregnancies than are 4 or 8 celled embryos.

Some (but not all) problems with embryos that prevent their developing into viable pregnancies will also prevent them from developing into blastocysts. Recently developed techniques enable use to better assess day one and day two embryos and thus some of the advantages of blastocyst culture can be achieved with other methods which can be used by a larger subgroup of patients. New culture media have recently been developed that enable us to develop a larger proportion of embryos into blastocysts in laboratory culture than previously. Some programs were hopeful that the use of day 5 blastocyst transfer would enable them to enhance their pregnancy rates while decreasing their high order multiple birth rates. Data on the value of blastocyst transfer has been mixed. My assessment of the literature is that blastocyst transfer decrease the pregnancy rate when applied to all patients. When blastocyst transfer is used in good prognosis patients, it decreases the high order multiple birth rate and replaces those multiple births with twins. Blastocyst transfer should be used when the plan is to only replace one embryo into the uterus.

In the best of situations, only a subset of embryos will develop into blastocysts. Many of those embryos which did not develop into blastocysts, if transferred into the uterus earlier, may have had the potential to become pregnancies. Patient age, response to the ovulation induction, and embryo quality are all variables that are correlated to getting pregnant without blastocyst transfer. Patients with a good response to the ovulation induction and good embryo quality are the patients for whom the data most clearly suggests that blastocyst transfer may be of benefit. The benefit of blastocyst transfer in patients with a poorer prognosis for traditional IVF has yet to be demonstrated. It has also been shown that blastocyst culture cannot completely select against chomosomally abnormal embryos (which would have been an important benefit).

Most programs that do a lot of blastocyst transfer use it for highly selected patients. Such patients generally do well, in terms of achieving pregnancy, no matter what technique is used. Some centers suggest that by choosing the faster growing embryos, one can safely decrease the number of embryos transferred on day 3 without a drop in pregnancy rates.

We feel that blastocyst transfer plays an important role in IVF. For good prognosis patients, it can be used to eliminate the risk of high order multiple births. Twins remain a significant problem. Blastocyst transfer is also necessary when embryo biopsy will be used to screen for genetic abnormalities (PGD).

We currently utilize blastocyst transfer in selected patients with the objective of decreasing the risk of multiple gestations when optimal selection of which embryos to transfer can't be made based on their growth pattern through day 3.