Changes in the freezing protocol for human zygotes alter embryonic development and pregnancy rates.
OBJECTIVE
To determine the effect of various freezing protocols on postthaw development and pregnancy rates resulting from transfer of human zygotes.


METHODS
Prospective study.


METHODS
Tertiary care center.


METHODS
Couples undergoing assisted reproductive technology (ART) procedures who wished to have their excess zygotes cryopreserved.


METHODS
We cryopreserved zygotes with one of three protocols.


METHODS
Post-thaw survival and development of the zygotes as well as pregnancy rate after transfer of these zygotes.


RESULTS
A 3-minute hold time after seeding, followed by a final preplunging temperature of -180 degrees C, resulted in a clinical pregnancy rate of 28.6%. In contrast, a 15-minute postseed hold time and a -30 degrees C final chamber temperature resulted in a 37.3% clinical pregnancy rate. When we combined the protocols to provide a 15-minute postseed holding time and a -180 degrees C before plunging into liquid nitrogen, we achieved a 69.6% clinical pregnancy rate.


CONCLUSIONS
By increasing the postseeding hold time and decreasing the temperature of the freezing chamber before plunging the zygotes into liquid nitrogen, significant improvements can be made in postthaw development and pregnancy rates.
Boone
William R
WR
Department of Obstetrics and Gynecology, Greenville Hospital System, South Carolina 29605-5601, USA. bboone@ghs.org
Crane
Martin M
MM
Johnson
Jane E
JE
Higdon
H Lee
HL
Blackhurst
Dawn W
DW
D000328:Adult; D015925:Cryopreservation; D047108:Embryonic Development; D005260:Female; D006801:Humans; D008875:Middle Aged; D011247:Pregnancy; D018873:Pregnancy Rate; D011446:Prospective Studies; D027724:Reproductive Techniques, Assisted; D015053:Zygote / Q000502:physiology*