Thread: frozen embryos
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Old 24th August 2009, 04:52 PM
Ron Conte Ron Conte is offline
Join Date: Jan 2006
Posts: 12,568

Another factor to consider.

The same SART RAND article states that, conservatively, as many as 65% of frozen embryos survive thawing.

But the statistics on number of transfers (of embryo into womb) versus number of live births do not reveal the number of frozen embyos that died in thawing. Obviously, when they thaw a number of embryos, they only transfer those that survive the thawing.

So in the best case statistic of a women under 35, using her own frozen eggs, the percentage of live births versus transfers is 33.6%. If 100 such embryos are thawed, at least 35 die prior to transfer, leaving 65 to be transferred to the womb, averaging 2.2 embryos per transfer, giving us 29.5 transfers. 66.4% of these transfers fail to produce any live birth.

Of frozen embryos, 87% are for use by patients plus about 2% that are donated to another couple. The rest are destroyed or are orphaned (can't determine who 'owns' the embryos; can't contact couple; dispute due to divorce, etc.)

35% die in thawing
43% (66.4% transfers of the 65% that survive thawing) die in the womb when there are no live births
for a subtotal of 78% deaths

22% survive thawing AND are associated with at least one live birth.

out of the 33.6% transfers that result in at least one live birth, some cases have one or two deaths of embryos (since usually 2 or 3 embryos are transferred). There is not enough information to determine what percentage of transferred embryos do not survive when there is at least one live birth, but the percentage of life births (for non-frozen embryos) with multiple infants born is only 34.9%, despite the fact that the average number of embryos transferred is over 2.

If about half die in the womb when there is at least one live birth, then the 22% drops to about 11%, meaning that 89% of frozen embryos that are thawed/transferred in an attempt to give them life die. This number could be higher, since clinics do not report the number of thawed embryos compared to the number transferred to the womb. Some embyros die in thawing, others might die in attempt to use IVF. Also, the number of deaths associated with live births is not clear.

These statistics are average numbers. The SART RAND study found that actual success rates in individual clinics varied very widely, from zero percent to 67%.
Ron Conte
Roman Catholic theologian
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