title: [Impact of age, single or double, fresh or frozen embryo transfer on pregnancy outcome after in vitro fertilization treatment].
abstract: OBJECTIVE
  To separately evaluate the embryo implantation rate (IR), clinical pregnancy rate and multiple pregnancy rate between women <38 years old or ≥ 38 years old in fresh or frozen thawed embryo transfer cycles, or in single or double embryo transfer cycles.
  
  
  METHODS
  A total of 7465 single or double embryo transfer cycles between January 2010 and December 2012 at Affiliated Sir Run Run Shaw Hospital, Zhejiang University were analyzed. There were 1546 single embryo transfer cycles and 5919 double embryo transfer cycles; 2447 fresh embryo transfer cycles and 5018 frozen-thawed embryo transfer cycles.
  
  
  RESULTS
  (1) Regardless of whether fresh or frozen-thawed embryo was used for transfer, there was no significant difference in embryo implantation rate between single and double embryo transfer groups in women <38 years. The clinical pregnancy rate significantly increased if double embryos were replaced (fresh embryo transfer, 53.3% vs 35.5%; frozen-thawed embryo transfer, 59.8% vs 38.0%, P < 0.01). Twin pregnancy rate also significantly increased (fresh embryo transfer, 28.7% vs 0.6%; frozen-thawed embryo transfer, 31.1% vs 3.0%, P < 0.01); (2) embryo implantation rate in fresh embryo transfer significantly increased in women ≥ 38 years old between groups of single or double embryo transfer (20.3% vs 9.5%, P < 0.05). No significant difference existed in IR for frozen-thawed embryo transfer. The clinical pregnancy rate significantly increased (P < 0.01) if double embryos were replaced (fresh embryo transfer, 33.2% vs 9.5%; frozen-thawed embryo transfer, 39.0% vs 21.1%, P < 0.01). Twin pregnancy rate was 19.4% in fresh embryo transfers versus 13.4% in frozen-thawed embryo transfers. There was no twin pregnancy in single embryo transfers.
  
  
  CONCLUSIONS
  Compared with single embryo transfer in women < 38 years, double embryo transfer can significantly increase the rates of clinical pregnancy nd twin pregnancy. Decision is made after thorough consultations and single embryo transfer is justifiable. Double embryo transfer is indicated for women ≥ 38 years.
authors.affiliation: Assisted Reproductive Unit, Department of Gynecology & Obstetrics, Affiliated Sir Run Run Shaw Hospital, School of Medicine, Zhejiang University, Hangzhou 310016, China.
authors.forename: Guo-fen
authors.initials: GF
authors.lastname: Wen
authors.affiliation: Assisted Reproductive Unit, Department of Gynecology & Obstetrics, Affiliated Sir Run Run Shaw Hospital, School of Medicine, Zhejiang University, Hangzhou 310016, China.
authors.forename: Xiao-ying
authors.initials: XY
authors.lastname: Jin
authors.affiliation: Assisted Reproductive Unit, Department of Gynecology & Obstetrics, Affiliated Sir Run Run Shaw Hospital, School of Medicine, Zhejiang University, Hangzhou 310016, China.
authors.forename: Zi-lian
authors.initials: ZL
authors.lastname: Wang
authors.affiliation: Assisted Reproductive Unit, Department of Gynecology & Obstetrics, Affiliated Sir Run Run Shaw Hospital, School of Medicine, Zhejiang University, Hangzhou 310016, China.
authors.forename: Qun
authors.initials: Q
authors.lastname: Wei
authors.affiliation: Assisted Reproductive Unit, Department of Gynecology & Obstetrics, Affiliated Sir Run Run Shaw Hospital, School of Medicine, Zhejiang University, Hangzhou 310016, China.
authors.forename: Feng
authors.initials: F
authors.lastname: Zhou
authors.affiliation: Assisted Reproductive Unit, Department of Gynecology & Obstetrics, Affiliated Sir Run Run Shaw Hospital, School of Medicine, Zhejiang University, Hangzhou 310016, China.
authors.forename: Chao
authors.initials: C
authors.lastname: Li
authors.affiliation: Assisted Reproductive Unit, Department of Gynecology & Obstetrics, Affiliated Sir Run Run Shaw Hospital, School of Medicine, Zhejiang University, Hangzhou 310016, China. Email: zhangsongying@126.com.
authors.forename: Song-ying
authors.initials: SY
authors.lastname: Zhang
mesh_terms: D000328:Adult; D000367:Age Factors; D015925:Cryopreservation; D004624:Embryo Transfer; D005260:Female; D006801:Humans; D011247:Pregnancy; D011256:Pregnancy Outcome; D018873:Pregnancy Rate; D011272:Pregnancy, Multiple; D012189:Retrospective Studies