title: Pregnancies following blastocyst stage transfer in PGD cycles at risk for beta-thalassaemic haemoglobinopathies.
abstract: BACKGROUND
  Preimplantation genetic diagnosis (PGD) usually involves blastomere biopsy 3 days post-insemination (p.i.), followed by genetic analysis and transfer of unaffected embryos later on day 3 or 4. We evaluate a strategy involving embryo biopsy on day 3 p.i., genetic analysis on day 4 and, following culture in blastocyst sequential media, transfer of unaffected embryos on day 5 p.i.
  
  
  METHODS
  PGD cycles were initiated in 15 couples at risk of transmitting beta-thalassaemia major. Oocyte retrieval and ICSI were performed according to standard protocols. Embryo culture used blastocyst sequential media. Embryos were biopsied on day 3 p.i. using acid Tyrode's for zona drilling, and the single blastomeres were genotyped by a protocol involving nested polymerase chain reaction and denaturing gradient gel electrophoresis analysis.
  
  
  RESULTS
  Forty of 109 (37%) embryos biopsied on day 3 p.i. developed to blastocysts by day 5 p.i., with at least one blastocyst available for transfer in 12 cycles (80%). Genotype analysis characterized 51/109 (47%) embryos unaffected for beta-thalassaemia major, of which 28 were blastocysts. Transfer of 37 day 5 p.i. embryos (blastocysts and non blastocysts) initiated eight clinical pregnancies. Implantation rate per embryo transferred was 12/37 (32%).
  
  
  CONCLUSIONS
  Embryo biopsy on day 3, followed by delayed transfer until day 5 p.i. offers a novel and effective strategy to overcome the time limit encountered when performing PGD, without compromising embryo implantation.
authors.affiliation: Embryogenesis Fertility Clinic, Kifissias Avenue, Athens 15125, Greece. gpalme@otenet.gr
authors.forename: G A
authors.initials: GA
authors.lastname: Palmer
authors.forename: J
authors.initials: J
authors.lastname: Traeger-Synodinos
authors.forename: S
authors.initials: S
authors.lastname: Davies
authors.forename: M
authors.initials: M
authors.lastname: Tzetis
authors.forename: C
authors.initials: C
authors.lastname: Vrettou
authors.forename: M
authors.initials: M
authors.lastname: Mastrominas
authors.forename: E
authors.initials: E
authors.lastname: Kanavakis
mesh_terms: D001706:Biopsy; D001755:Blastocyst; D003470:Culture Media; D004624:Embryo Transfer; D005260:Female; D005307:Fertilization in Vitro; D020022:Genetic Predisposition to Disease; D005838:Genotype; D006579:Heterozygote; D006801:Humans; D008297:Male; D009924:Organ Culture Techniques; D016133:Polymerase Chain Reaction; D011247:Pregnancy; D011256:Pregnancy Outcome; D019836:Preimplantation Diagnosis; D020554:Sperm Injections, Intracytoplasmic; D013997:Time Factors; D017086:beta-Thalassemia / Q000175:diagnosis* / Q000235:genetics*
chemical_list: D003470:Culture Media