Going to Blast!

“Going to blast” is different than “having a blast.” When your RE talks about going to blast he/she is referring to the stage of embryo development at the time of the embryo transfer. When I began practicing infertility in 1996 most embryo transfers were done on the second day after egg collection (egg collection is day zero). However, most clinics moved rapidly to day 3 ET to allow for better embryo selection. The move to day 5 ET was a bit more difficult as commercially available media was a problem and by media I am not referring to CD or DVD but to the liquid that embryos are cultured in after retrieval of the eggs. Now many clinics have had very good success with day 5 ET and it has become more common. So today’s question is the simple one whereas tomorrow we will deal with the pro/cons of blast transfer. Of course, if you are dying to hear the next question you can always run down to your corner bookstore and purchase “100 Questions and Answers about Infertility.” There are a couple of copies left at the Barnes and Noble at Clarendon (Arlington, VA)…I know because I put them on the shelf (actually, I didn’t but I admit that the thought crossed my mind).

69. What is a blastocyst transfer?

Embryos on the third day after egg collection are referred to as cleavage-stage embryos. At this point, each embryo contains 6 to 10 discreet cells (blastomeres). When assessing these embryos for quality, the embryologist grades them based on the number and appearance of the blastomeres. Embryos that have equal-size blastomeres with no fragmentation are usually given a high grade, whereas embryos that have extensive fragmentation with unequal-size blastomeres are given a low grade. In general, higher-grade embryos have a much better chance of implanting successfully and generating a pregnancy. If the embryos are maintained in culture beyond day 3, they first form a solid ball containing approximately 30 to 50 cells, called a morula. Over the next day or two, this solid ball of cells becomes a hollow sphere with a clearly defined inner cell mass. This hollow ball of cells is called a blastocyst. Many clinics maintain the embryos in culture until the fifth day to allow for improved selection of embryos to transfer. Patients who undergo an embryo transfer on day 5 or 6 after egg collection are referred to as having a blastocyst transfer.