How Many Embryos Are Left Over?
The Los Angeles Times series on frozen embryos (discussed yesterday) says that "almost 500,000" embryos are in freezers. That's consistent with a 2003 RAND study, which estimated "nearly 400,000." But how many become available each year?
No one seems to know. The Centers for Disease Control (CDC) do not publish data on embryo creation or disposal. Still, we can use the data available to suggest very roughly how many potentially viable unused embryos are either stored or destroyed each year in the course of fertility treatment.
Assumptions:
- Only eggs from women under 35 are considered (for quality reasons).
- Fifteen eggs are generated in a successful cycle (the middle of this range).
- Half the recovered eggs are fertilized (a guess).
Facts:
- 41,302 women under 35 underwent a cycle of hormone treatment in the U.S in 2005, the most recent year for which data is available.
- 92% had eggs successfully retrieved = 37,998 women.
- An average of 2.4 embryos were transferred per woman under 35.
Calculations:
284,985 embryos were created, and 91,195 transferred. Thus a gross total of 193,790 embryos were left over. But far fewer are available.
A full 63% of the women who started cycles in 2005 did not achieve a successful live birth, so the RAND estimate that 88.2% were reserved for "future family building" seems plausible. Indeed, if we accept their conclusion that only 2.8% of frozen embryos are actually available for research, the annual number would be only 5,426.
This is absolutely a back-of-the-envelope calculation. A conscious effort to encourage donation might raise it, as would higher egg retrieval and fertilization rates. But it's hard to see more than 20,000 a year being available nationally.
Of course, when Harvard cannot find ten in two years, even 5,000 sounds like a large number.
Previously on Biopolitical Times: