Yesterday the American Society of Reproductive Medicine and the Society for Assisted Reproductive Technology released revised guidelines for the number of embryos transferred during assisted reproductive therapies, recommending the transfer of no more than two embryos during a single procedure for women younger than age 35. In 1999, the ASRM had released guidelines recommending the transfer of only two embryos for women younger than age 35 with a "healthy" prognosis and three embryos for women with a poorer prognosis for successful implantation. The recommendation rises to as many as four embryos for patients aged 38 to 40 and to five embryos for women over the ago of 40.
Today more than a third of pregnancies conceived using assisted reproductive technology result in a multiple birth. Multiple embryo transfer has also contributed to what are now more than a half million frozen stored embryos awaiting: future use, "adoption," stem cell research or, for most, destruction.