Prognostic factors for the success rate of embryo freezing |
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Authors: | Karlstrom PO; Bergh T; Forsberg AS; Sandkvist U; Wikland M |
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Institution: | Carl von Linne Kliniken, Uppsala, Sweden. |
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Abstract: | To find some prognostic factors for the outcome of frozen-thawed cycles, we
have retrospectively analysed all frozen pre-embryos that were thawed
during 1993 and 1994 at two in-vitro fertilization (IVF) units in Sweden.
Supernumerary pre-embryos were frozen from 551 oocyte retrievals and these
resulted in 660 frozen-thawed cycles which lead to 623 thawed embryo
transfers. The outcome of these transfers was 137 clinical pregnancies with
a pregnancy rate of 22% per frozen-thawed embryo transfers. Women <40
years of age had a higher birth rate than those > or =40 years, 19 and
5% respectively (P < 0.01). Transfers with two and three pre-embryos
resulted in pregnancy rates of 23 and 27%, respectively, compared with 14%
for transfer of one embryo. A pregnancy resulting from the initial embryo
transfers had a predictive value for results of the subsequent
frozen-thawed cycle. Embryo grade and cleavage stage at the time of
freezing was important for the survival of the frozen-thawed pre-embryos.
The pregnancy rate was not influenced by the cleavage stage, but a tendency
toward a lower pregnancy rate was seen for the embryos with lower grading.
To conclude, cryopreservation seems to be beneficial in women <40 years
of age, who have supernumerary pre-embryos of good quality for freezing and
of which at least two can be transferred.
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