title: Factors related to clinical pregnancy after vitrified-warmed embryo transfer: a retrospective and multivariate logistic regression analysis of 2313 transfer cycles.
abstract: OBJECTIVE
  What factors does multivariate logistic regression show to be significantly associated with the likelihood of clinical pregnancy in vitrified-warmed embryo transfer (VET) cycles?
  
  
  CONCLUSIONS
  Assisted hatching (AH) and if the reason to freeze embryos was to avoid the risk of ovarian hyperstimulation syndrome (OHSS) were significantly positively associated with a greater likelihood of clinical pregnancy.
  
  
  BACKGROUND
  Single factor analysis has shown AH, number of embryos transferred and the reason of freezing for OHSS to be positively and damaged blastomere to be negatively significantly associated with the chance of clinical pregnancy after VET. It remains unclear what factors would be significant after multivariate analysis.
  
  
  METHODS
  The study was a retrospective analysis of 2313 VET cycles from 1481 patients performed between January 2008 and April 2012. A multivariate logistic regression analysis was performed to identify the factors to affect clinical pregnancy outcome of VET.
  
  
  METHODS
  There were 22 candidate variables selected based on clinical experiences and the literature. With the thresholds of α entry = α removal= 0.05 for both variable entry and variable removal, eight variables were chosen to contribute the multivariable model by the bootstrap stepwise variable selection algorithm (n = 1000). Eight variables were age at controlled ovarian hyperstimulation (COH), reason for freezing, AH, endometrial thickness, damaged blastomere, number of embryos transferred, number of good-quality embryos, and blood presence on transfer catheter. A descriptive comparison of the relative importance was accomplished by the proportion of explained variation (PEV).
  
  
  RESULTS
  Among the reasons for freezing, the OHSS group showed a higher OR than the surplus embryo group when compared with other reasons for VET groups (OHSS versus Other, OR: 2.145; CI: 1.4-3.286; Surplus embryos versus Other, OR: 1.152; CI: 0.761-1.743) and high PEV (marginal 2.77%, P = 0.2911; partial 1.68%; CI of area under receptor operator characteristic curve (ROC): 0.5576-0.6000). AH also showed a high OR (OR: 2.105, CI: 1.554-2.85) and high PEV (marginal 1.97%; partial 1.02%; CI of area under ROC: 0.5344-0.5647). The number of good-quality embryos showed the highest marginal PEV and partial PEV (marginal 3.91%, partial 2.28%; CI of area under ROC: 0.5886-0.6343).
  
  
  CONCLUSIONS
  This was a retrospective multivariate analysis of the data obtained in 5 years from a single IVF center. Repeated cycles in the same woman were treated as independent observations, which could introduce bias. Results are based on clinical pregnancy and not live births. Prospective analysis of a larger data set from a multicenter study based on live births is necessary to confirm the findings.
  
  
  CONCLUSIONS
  Paying attention to the quality of embryos, the number of good embryos, AH and the reasons for freezing that are associated with clinical pregnancy after VET will assist the improvement of success rates.
authors.affiliation: Assisted Reproduction Center, Maternal & Child Health Care Hospital of Shaanxi Province, Hou Zai Men 73# Xin Cheng District, Xi'an, China.
authors.forename: Wenhao
authors.initials: W
authors.lastname: Shi
authors.forename: Silin
authors.initials: S
authors.lastname: Zhang
authors.forename: Wanqiu
authors.initials: W
authors.lastname: Zhao
authors.forename: Xue
authors.initials: X
authors.lastname: Xia
authors.forename: Min
authors.initials: M
authors.lastname: Wang
authors.forename: Hui
authors.initials: H
authors.lastname: Wang
authors.forename: Haiyan
authors.initials: H
authors.lastname: Bai
authors.forename: Juanzi
authors.initials: J
authors.lastname: Shi
mesh_terms: D000328:Adult; D000367:Age Factors; D015925:Cryopreservation; D004624:Embryo Transfer; D005260:Female; D006801:Humans; D016015:Logistic Models; D015999:Multivariate Analysis; D011247:Pregnancy; D011256:Pregnancy Outcome; D012189:Retrospective Studies
keywords: clinical pregnancy; multivariate logistic regression analysis; vitrified–warmed embryo transfer (VET)