title: Initial experience with extended culture and blastocyst transfer of cryopreserved embryos.
abstract: OBJECTIVE
  Our purpose was to evaluate the viability and transfer efficiency of cryopreserved embryos allowed to develop into blastocysts in extended culture for in vitro fertilization.
  
  
  METHODS
  The embryos for in vitro fertilization that had been cryopreserved at either 2 PN (pronuclear) or cleaving stage (day 1-3) were thawed and cultured for uterine transfer on day 5. Outcome for day 5 embryo transfer was prospectively compared with previous outcomes from embryos transferred on day 2 or 3.
  
  
  RESULTS
  For embryos thawed and transferred on day 2 or 3 (n = 99), the pregnancy rate was 33%, the implantation rate per embryo transferred was 15.2%, and the rate of multiple gestations was 42.4% (14/33) with 35.7% of pregnancies having >/=3 gestational sacs. For extended culture embryos transferred on day 5 (n = 25), the pregnancy rate was 36%, the implantation rate per embryo transferred was 16.7%, and the rate of multiple gestations was 33.3% (3/9) with all of these being twins. For embryo transfers performed on day 5 in which only blastocysts were transferred (n = 9), the pregnancy rate was 66.7%, the implantation rate per blastocyst was 44.4% (greater than the rate for the day 2 or 3 embryos, P =.0043), and the rate of multiple gestations was 33.3% (2/6) with all of these being twins. In extended culture 29.8% of cryopreserved embryos progressed to the blastocyst stage. In this series 4 subjects (15.4%) did not have blastocysts by day 5.
  
  
  CONCLUSIONS
  Acceptable pregnancy rates can be obtained from cryopreserved embryos cultured to the blastocyst stage with a significantly higher implantation rate. Transfer of embryos that have "self-selected" to blastocysts results in reduced risk of higher-order (>2) multiple gestations, because only 1 or 2 embryos are transferred.
authors.affiliation: Division of Reproductive Endocrinology, Department of Obstetrics and Gynecology, Oregon Health Sciences University, Portland, USA.
authors.forename: M J
authors.initials: MJ
authors.lastname: Gorrill
authors.forename: P F
authors.initials: PF
authors.lastname: Kaplan
authors.forename: P E
authors.initials: PE
authors.lastname: Patton
authors.forename: K A
authors.initials: KA
authors.lastname: Burry
mesh_terms: D001755:Blastocyst / Q000502:physiology*; D015925:Cryopreservation; D046508:Culture Techniques; D010064:Embryo Implantation; D004624:Embryo Transfer; D005260:Female; D005307:Fertilization in Vitro; D006801:Humans; D011247:Pregnancy; D011272:Pregnancy, Multiple; D013997:Time Factors