In The Field

The aging egg

I’m reporting from the American Society for Reproductive Medicine annual meeting this week, in Washington D.C. There are sure to be some controversial subjects discussed including the ethics and efficacy of prenatal genetic screening in assisted reproductive technology (ART), as well as a hot up and coming topic in the cryopreservation of eggs. In press conferences held this morning however, the interesting topic was a growing concern in ART, and one that has some controversial implications internationally. Timothy Hickman, medical director at Houston IVF in Texas, and others were discussing the justifications for transferring multiple embryos in older women.

The danger implicit in transferring, say six embryos as opposed to two, is generally multiple births, something that stands to threaten the health of older women. Nevertheless, the eggs of older women are sometimes of questionable quality, riddled by aneuploidy and other factors that enhance the likelihood for miscarriage and failed pregnancy.

So, the trick is optimizing the number of embryos that should be implanted in an older woman so that the success rate of single births is sufficiently high and the rate of multiple births stays relatively low. Current recommendations for women above the age of 40 is no more than five cleavage stage embryos and no more than three blastocyst stage (more developed) embryos.

Hickman talked about a mathematical model that could predict at different ages what the precise rates of single and multiple births. By setting the threshold for triplet births at around 1%, he showed that indeed, the number of embryos delivered could be increased to as many as six without increasing the triplet birth rate above that threshold.

In more than 240 cycles of ART that he looked at in women aged 41-42, this model held up and predicted that in women over forty as many as six embryos could be transferred to increase the success rate up to nearly 45% percent.

This is controversial, as clinics in many European countries are restricted by law in the number they can transfer. Hickman told me “There are some arbitrary laws in the UK saying that doctors can transfer no more than two. The physicians there are very frustrated.”

Judy Stern, at Dartmouth-Hitchcock Medical center in Lebanon New Hampshire, has started delving into data from the Society for Assisted Reproductive Technology or SART database. She was able to look at thousands of IVF cycles and looked for variables that predicted how successful embryo delivery would be in aging women. Oddly Folicle stimulating hormone, which is currently used in guidelines to determine how many embryos to implant, proved not to be predictive of outcome. Other variables like the number of eggs collected from the woman made a differenc, and there were distinct differences in women 38 and older and women 40 and older, something that is not accounted for under current guidelines.

Stern says she’s had trouble convincing docs in her own clinic to start making decisions based on these more predictive factors.


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