title: Vitrification can modify embryo cleavage stage after warming. Should we change endometrial preparation?
abstract: OBJECTIVE
  Studies have shown that embryo metabolism and cell cleavage after warming vitrified embryos is faster than after thawing frozen embryos. We study vitrified embryo transfer (VET) results depending on the developmental stage of warmed embryos and the duration of progesterone treatment before embryo transfer.
  
  
  METHODS
  We designed a prospective study, patients were randomized in two groups, starting progesterone three (D + 3) or four days (D + 4) before embryo transfer. We recruited 88 patients with embryos vitrified on day 3.
  
  
  RESULTS
  We didn't find statitistical differences in pregnancy rate when we transferred embryos in D + 3 vs D + 4 (38.2 % vs 40.5 % p ≥ 0.05). The day after warming, 54.6 % of embryos had developed to morula or early blastocyst, 32.4 % to cleavage stage and 13 % didn't cleave. Transfers were with morula/blastocysts stage embryos (52.1 %; n:37), cleavage stage embryos (18.3 %; n:13) or mixed (29.6 %; n:21). Implantation rate was significantly higher in morula/blastocyst stage than in cleavage stage or mixed transfers (44 %, 22 % and 16.3 %; p = 0.011). Pregnancy and implantation rates were significantly higher in morula/blastocyst transfers on D + 4 than on D + 3 (68.7 % and 64.7 % vs 33.3 %, and 33.3 %, p = 0.033 and p = 0.034).
  
  
  CONCLUSIONS
  Our findings suggest that a majority of embryos will develop to morula/blastocyst stage after warming. VET results with morula/blastocysts, and after four days of progesterone supplementation, are better than with cleavage stage embryos.
authors.affiliation: URH García del Real, 30 Ana Teresa St., Madrid, 28023, Spain. rcercas@urh.es
authors.forename: R
authors.initials: R
authors.lastname: Cercas
authors.forename: C
authors.initials: C
authors.lastname: Villas
authors.forename: I
authors.initials: I
authors.lastname: Pons
authors.forename: C
authors.initials: C
authors.lastname: Braña
authors.forename: S
authors.initials: S
authors.lastname: Fernandez-Shaw
mesh_terms: D000328:Adult; D001755:Blastocyst / Q000166:cytology / Q000502:physiology; D002970:Cleavage Stage, Ovum / Q000166:cytology / Q000502:physiology; D015925:Cryopreservation / Q000379:methods*; D046149:Embryo Culture Techniques; D010064:Embryo Implantation; D004624:Embryo Transfer / Q000379:methods*; D047108:Embryonic Development; D005260:Female; D006801:Humans; D009028:Morula / Q000166:cytology / Q000502:physiology; D011247:Pregnancy; D018873:Pregnancy Rate; D011446:Prospective Studies; D058989:Vitrification