title: Improved implantation rate after chemical removal of the zona pellucida.
abstract: OBJECTIVE
  To evaluate the implantation rate achieved after chemical removal of the zona pellucida from day 5 human in vitro-derived embryos.
  
  
  METHODS
  Prospective, randomized, controlled study.
  
  
  METHODS
  A tertiary care infertility clinic.
  
  
  METHODS
  Two hundred fifty-seven patients undergoing IVF with transfer of morulas or blastocysts on day 5 after oocyte retrieval. All patients had had at least two previous implantation failures.
  
  
  METHODS
  Chemical removal of zona pellucida by using acidic Tyrode's solution vs. no removal (controls).
  
  
  METHODS
  Clinical pregnancy rate and implantation rate per transfer.
  
  
  RESULTS
  Embryos without zona pellucida implanted at nearly twice the rate of control embryos (15.7% vs. 27.5%). The pregnancy rate was also significantly higher in the zona pellucida-free group than the control group (31.0% vs. 46.1%). Removal of zona pellucida was most effective in embryos with delayed development, which reached the morula or early cavitating stage on day 5 of in vitro culture (implantation rate, 12.1% vs. 25.7%).
  
  
  CONCLUSIONS
  Chemical removal of zona pellucida from day 5 in vitro cultured human embryos is an effective and safe method of significantly improving the implantation rate, especially of embryos with delayed development.
authors.affiliation: Gynecology and Obstetrics Department and General Faculty Hospital, Charles University, Prague, Czech Republic. ljeli@seznam.cz
authors.forename: Ladislava
authors.initials: L
authors.lastname: Jelinkova
authors.forename: Jana
authors.initials: J
authors.lastname: Pavelkova
authors.forename: Erwin
authors.initials: E
authors.lastname: Strehler
authors.forename: Wolfgang
authors.initials: W
authors.lastname: Paulus
authors.forename: Jaroslav
authors.initials: J
authors.lastname: Zivny
authors.forename: Karl
authors.initials: K
authors.lastname: Sterzik
mesh_terms: D001755:Blastocyst / Q000502:physiology; D010064:Embryo Implantation; D005260:Female; D006801:Humans; D007552:Isotonic Solutions / Q000494:pharmacology; D011247:Pregnancy; D011446:Prospective Studies; D020554:Sperm Injections, Intracytoplasmic; D015044:Zona Pellucida / Q000187:drug effects / Q000502:physiology*
chemical_list: D007552:Isotonic Solutions; C037692:Tyrode's solution