title: [Study of the best embryo transfer strategy in frozen-thawed embryo transfer cycle].
abstract: OBJECTIVE
  To study the relationship of the number and quality of embryos transferred with clinical pregnancy rate and multiple pregnancy rate in frozen-thawed embryo transfer (FET) cycle.
  
  
  METHODS
  Retrospective analysis of the clinical data of 995 FET cycles. Patients were stratified as age < 35 or > or = 35, Both groups' clinical pregnancy rate and multiple pregnancy rate were compared according to the number of embryos and high-quality embryos transferred.
  
  
  RESULTS
  (1) The clinical pregnancy rates were 50.0%, 56.6% and 56.5%, and twin pregnancy rates were 6.3%, 43.8% and 30.6% respectively in < 35 group when one, two or three embryos were transferred. There is not any significantly statistic difference among these subgroups (P > 0.05). However, the twin pregnancy rate in one-embryo transferred subgroup was significantly lower than that of two-embryo transferred subgroup (P < 0.05). Moreover, the clinical pregnancy rate was not different among single high-quality embryo transferred subgroup and other high-quality embryo transferred subgroups, the multiple pregnancy rate was lower than the others. (2) The clinical pregnancy rates were 0, 47.3% and 53.8%, and twin pregnancy rates were 0, 25.7% and 25.7% respectively in > or = 35 group when one, two or three embryos were transferred. The clinical pregnancy rate and twin pregnancy rate between two-embryo and three-embryo transferred subgroups were not significantly different (P > 0.05). Moreover, the clinical pregnancy rate was not different among two-embryo transferred containing one high-quality embryo subgroup and other high-quality embryo transferred subgroups, the multiple pregnancy rate was lower than the others.
  
  
  CONCLUSIONS
  There is a close relationship between the number and quality of embryos transferred and clinical pregnancy rate, multiple pregnancy rate in FET cycles. For the patient aged < 35, we recommend performing single high-quality embryo transfer in order to reduce the multiple pregnancy. For the patient aged > or = 35, two-embryo transfer containing one high-quality embryo is enough to obtain a satisfied clinical pregnancy rate and an acceptable multiple pregnancy rate.
authors.affiliation: Reproductive Medicine Center, Institute of Clinical Medicine, Sir Run Run Shaw Hospital, Medical School Zhejiang University, Hangzhou 310016, China.
authors.forename: Tao
authors.initials: T
authors.lastname: Song
authors.forename: Feng
authors.initials: F
authors.lastname: Zhou
authors.forename: Liu
authors.initials: L
authors.lastname: Liu
authors.forename: Xiao-Na
authors.initials: XN
authors.lastname: Lin
authors.forename: Song-Ying
authors.initials: SY
authors.lastname: Zhang
mesh_terms: D000328:Adult; D015925:Cryopreservation; D004624:Embryo Transfer / Q000379:methods*; D005260:Female; D006801:Humans; D008875:Middle Aged; D011247:Pregnancy; D018873:Pregnancy Rate; D011272:Pregnancy, Multiple; D012189:Retrospective Studies; D055815:Young Adult