A successful human oocyte cryopreservation regime: survival,
implantation and pregnancy rates are comparable to that of cryopreserved
embryos generated from sibling oocytes.
DS Yang, PL Blohm, L Cramer, K Nguyen, YL Zhao and KL
Winslow. Florida Institute for Reproductive Medicine,
Objectives: We reported last year (Yang et al., Fertility &
Sterility Vol. 70 suppl. 1. 1998, P S86) that our
specially developed oocyte cryopreservation regime significantly improved the cryosurvival rate of human fresh and unfertilized MII
oocytes compared to oocyte cryopreservation utilizing traditional embryo
cryopreservation protocol. To further assess the efficiency of the protocol,
this study was designed to examine the survival, fertilization, implantation,
and pregnancy rates of cryopreserved oocytes based on cumulated clinical cases,
and to compare these rates to those of sibling fresh oocytes and cryopreserved
embryos obtained from the same cycles.
Design: Prospective descriptive clinical
study. Oocytes from donors and patients were used for the study.
Materials and Methods: One hundred and twenty oocytes (fifty
from donors out of 10 fresh cycles and seventy from patients out of 7 fresh
cycles) collected after controlled ovarian stimulation went through the oocyte
cryopreservation process. The oocytes were pre-equilibrated in 1.5M PROH while
cooling from 370C to 320C over 5 minutes, and then frozen in 1.5M PROH with
0.2M sucrose. The oocytes were then stored in liquid nitrogen for 1 to 12
months. After thawing, the cryoprotectants were
removed by stepwise dilution and the survived oocytes were cultured for 1 to 2
hours before ICSI. Fertilization (2PN) was confirmed 16 to 18 hours after ICSI
and embryo transfer was carried out next day. The protocol for preparation of
the endometrium was identical to that used for cryopreserved embryo transfer.
Positive pregnancy tests were confirmed by ultrasound examination four weeks
after embryo transfer.
Results: The outcome of cryopreserved oocytes
is illustrated on the table.
|
Oocyte
origin |
Thawing
cycles (n) |
MII thawed
(n) |
Survival (%) |
ICSIed
(n) |
# of 2PN (%) |
ET cycle (n) |
# Embryos
trans. |
Clinical preg. (%) |
Implantation
(%) |
|
Donor |
9 |
50 |
64.0% |
31 |
26 (83.9%) |
9 |
24 |
5 (55.6%) |
8 (33.3%) |
|
Patient |
8 |
70 |
52.9% |
37 |
28 (75.7%) |
8 |
27 |
2 (25.0%) |
3 (11.1%) |
|
Total |
17 |
120 |
57.5% |
68 |
54 (79.4%) |
17 |
51 |
7 (41.2%) |
11 (21.6%) |
Two sets of healthy twins have been
born, and 4 additional ongoing pregnancies have been established. The
fertilization rate of cryopreserved oocytes (79.4%) is similar to that of fresh
sibling oocytes obtained from the same cycle (85.2%, 150/176, P=0.823). The
survival, implantation and pregnancy rates of cryopreserved oocytes are
comparable to those of frozen embryos (60.5%, 57.1% and 18.5%, respectively,
P>0.1) generated from the same cycles.
Conclusions: In this study, cryopreserved oocytes
achieved fertilization, survival, embryo development and pregnancy rates
comparable to their fresh sibling oocytes and cryopreserved embryos. It is
thought that the increased equilibration temperature and sucrose concentration
in freezing solution is responsible for the successful oocyte cryopreservation.
These data suggest that the human oocyte cryopreservation regime reported here
is as efficient as our current embryo cryopreservation program.