Comparison of vitrification and conventional slow freezing for cryopreservation of ovarian tissue with respect to the number of intact primordial follicles: A meta-analysis.
BACKGROUND
Vitrification is the standard method for cryopreserving human oocytes and embryos, but its effects on ovarian tissue are uncertain. The purpose of this meta-analysis was to compare the proportion of intact primordial follicles in ovarian tissue cryopreserved with vitrification versus slow freezing.


METHODS
Medline, Cochrane, EMBASE, and Google Scholar databases were searched until November 11, 2014 using combinations of the search terms: ovarian tissue, cryopreservation, vitrification, follicle, follicles. Inclusion criteria were randomized controlled trails, two-arm prospective studies, and retrospective studies in which ovarian tissues were preserved by vitrification or conventional slow freezing. The primary outcome was the proportion of intact primordial follicles.


RESULTS
Six studies were included in the meta-analysis. The number of patients ranged from 3 to 20, and age ranged from 20 to 43 years. Total number of morphologically intact follicles ranged from 14 to 2058, among which 6 to 724 were primordial. The pooled odds ratio (OR) showed no significant difference in the proportion of intact primordial follicles after slow freezing or vitrification (OR = 1.228, 95% confidence interval [CI]: 0.769-1.961, P = 0.390). Sensitivity analysis using the leave-one-out approach indicated no considerable changes in the direction and magnitude of the pooled estimates when individual studies were excluded one at a time, indicating good reliability of the current analysis.


CONCLUSIONS
Vitrification and slow freezing produce equivalent results with respect to intact primordial follicles for the cryopreservation of human ovarian tissue. However, the included studies varied in the cryopreservation protocols used.
aDepartment of Gynecology bDepartment of General Surgery, First Affiliated Hospital, School of Medicine, Zhejiang University, Hangzhou 310003, China.
Xin-Hui
XH
Zhou
Dan
D
Zhang
Jin
J
Shi
Yi-Jun
YJ
Wu
D000328:Adult; D015925:Cryopreservation / Q000379:methods*; D005260:Female; D005615:Freezing; D006801:Humans; D016017:Odds Ratio; D006080:Ovarian Follicle / Q000166:cytology; D010053:Ovary / Q000166:cytology*; D015203:Reproducibility of Results; D058989:Vitrification
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