title: Effect of vitrification versus slow freezing of human day 3 embryos on β-hCG levels.
abstract: OBJECTIVE
  The study was designed to investigate the effect of vitrification and slow freezing for the cryopreservation of human day 3 embryos on serum β-hCG levels in pregnancies established after frozen embryo transfer (FET).
  
  
  METHODS
  Of the 1384 FET cycles initiated, 1131 embryo transfers met study criteria and assigned to one of two groups: 797 slow-freezing embryo transfers or 334 vitrified embryo transfers. Median values of β-hCG and outcome of all pregnancies were compared between the two groups. Predictive values of serum β-hCG on day 12 after embryo transfer for establishing ongoing pregnancy and pregnancy failure were determined by receiver operating characteristic (ROC) curve analysis.
  
  
  RESULTS
  In the slow-freezing group, 383 ongoing pregnancies occurred (48.1 %), and transfers of vitrified embryos resulted in 154 pregnancies (46.1 %). Median β-hCG values (279.2 IU/L) for ongoing pregnancies after transfer of vitrified embryos were significantly lower than that of slow frozen embryos (320.5 IU/L). The median values of β-hCG for singleton in the two groups was statistically significant (P <0.05). For slow-freezing embryo transfers, the cut-off value of β-hCG in predicting ongoing pregnancy was 147 IU/L (sensitivity 88.3 %, specificity 80.7 %). For vitrified embryo transfers, the value was 135 IU/L (sensitivity 84.4 %, specificity 76.3 %).
  
  
  CONCLUSIONS
  Day 12 β-hCG levels after FET are significantly affected by the methods of embryo cryopreservation for ongoing pregnancies. Furthermore, when using β-hCG cut-off value to assess pregnancy outcome, the cryopreservation methods should be taken into account.
authors.affiliation: Reproductive Medicine Center, Department of Obstetrics and Gynecology, Sir Run Run Shaw Hospital, College of Medicine, Zhejiang University, No. 3, Qingchun Road, Hangzhou, 310016, China.
authors.forename: Yamei
authors.initials: Y
authors.lastname: Xue
authors.forename: Xiaomei
authors.initials: X
authors.lastname: Tong
authors.forename: Lingying
authors.initials: L
authors.lastname: Jiang
authors.forename: Haiyan
authors.initials: H
authors.lastname: Zhu
authors.forename: Lingyun
authors.initials: L
authors.lastname: Yang
authors.forename: Songying
authors.initials: S
authors.lastname: Zhang
mesh_terms: D000328:Adult; D018997:Chorionic Gonadotropin, beta Subunit, Human / Q000097:blood*; D015925:Cryopreservation / Q000379:methods*; D004622:Embryo, Mammalian / Q000166:cytology*; D005260:Female; D005307:Fertilization in Vitro / Q000379:methods*; D005615:Freezing; D006801:Humans; D007246:Infertility / Q000097:blood / Q000175:diagnosis*; D011247:Pregnancy; D011256:Pregnancy Outcome; D012372:ROC Curve; D058989:Vitrification
chemical_list: D018997:Chorionic Gonadotropin, beta Subunit, Human