[Effects of cryopreservation time and thawing method of human oocyte vitrification on the outcome of assisted reproduction]

Abstract

Objective: To evaluate the effects on pregnancy outcome of freezing time from oocyte retrieval and thawing method for metaphaseII human oocytes vitrification.

Methods: From Mar 2007 to Mar 2009, the clinical outcome of 30 infertile women undergoing vitrified-thawing oocytes of in vitro fertilization-embryo transfer (IVF-ET) in the Reproductive Medical Center of the First Affiliated Hospital of Zhengzhou University was studied retrospectively, including 21 women with double fallopian tube obstruction and 9 women's husband azoospermia. All infertile women were divided into three groups, including 5 cases in group A (freezing between 4 and 5 hours from oocyte retrieval and conventional thawing method), 9 cases in group B (freezing within 2 hours from retrieval and conventional thawing method) and 16 cases in group C (freezing within 2 hours from retrieval and improved thawing method). The vitrified oocytes were preserved for 2 months to 1 year and thawed for Intracytoplasmic sperm injection (ICSI) and embryo transfer. The outcome of IVF and pregnancy were recorded.

Results: (1) The rates of oocyte survival was (65 ± 33)% in group B and (72 ± 23)% in group C and the rate of transfer cycle was 9/9 in group B and 16/16 in group C, which were all significantly higher than (16 ± 17)% of oocyte survival and 1/5 of transfer cycle in group A (P = 0.001, 0.021). However, the rate of oocyte survival and transfer cycle between group B and group C did not reach statistical difference (P > 0.05). The rate of implantation and clinical pregnancy of (33 ± 38)% and 9/16 in group C were significantly higher (4 ± 11)% and 1/9 in group B (P = 0.033, 0.040). (2) The mean age of women in group C were (28.6 ± 2.1) in oneself oocyte, (28.0 ± 4.6) in donor oocyte and (28.1 ± 3.4) in donor sperm. The rate of oocyte survival was (73 ± 25)%, (88 ± 10)% and (66 ± 25)%. The rate of fertilization rate was (84.6 ± 0.9)%, (79.3 ± 2.0)% and (82.8 ± 15.0)%. The rate of implantation was (20.0 ± 44.7)%, (33.0 ± 0.1)%, (41.6 ± 41.7)%. The rate of clinical pregnancy was 1/5 in oneself cycles, 3/3 in donor oocyte cycles, 5/8 banked donor sperm cycles in group C. All above clinical parameters were not statistically different (P > 0.05). (3) In group A, one women underwent IVF-ET and no clinical pregnancy was observed. One women pregnancy was terminated at two months in group B. The clinical pregnancies rate of group C was 9/16, late abortion occurred in 1 woman, the other 8 women underwent term pregnancy, including 5 male infants and 4 female infants. All of infants showed normal Karyotype. Live-birth rates per warmed oocyte was 5.9%(8/135). The mean gestational weeks and birth weight of the infants were (39.4 ± 0.9) weeks and (3574 ± 569) g, respectively.

Conclusions: Embryo quality and clinical outcome of thawing cycles could be significantly improved when oocyte vitrification was performed within 2 hours from oocyte retrieval and improved thawing method.