title: Is frozen embryo transfer cycle associated with a significantly lower incidence of ectopic pregnancy? An analysis of more than 30,000 cycles.
abstract: OBJECTIVE
  To analyze the incidence of ectopic pregnancy (EP) in fresh compared with frozen-thawed cycles.
  
  
  METHODS
  Retrospective cohort study.
  
  
  METHODS
  Teaching hospital.
  
  
  METHODS
  Thirty-one thousand nine hundred twenty-five women undergoing in vitro fertilization-embryo transfer (IVF-ET) from January 2006 to December 2013.
  
  
  METHODS
  Fresh IVF-ET compared with frozen-thawed ET (FET).
  
  
  METHODS
  Incidence of EP with fresh IVF-ET compared with frozen-thawed ET cycles, clinical pregnancy rate, and rate of EP per clinical pregnancy.
  
  
  RESULTS
  For the fresh IVF cycles, 19,173 patients underwent oocyte retrieval; 15,042 had an ET, 6,431 of these patients (42.7%) had a clinical pregnancy, and among these 297 (1.97%) appeared to have an EP. The group of patients undergoing frozen-thawed ET (12,752 patients) included 12,255; there were 5,564 pregnancies (45.4%) and 124 ectopic implants (1.01%). The incidence of an EP per clinical pregnancy was 4.62% for the fresh transfer group compared with 2.22% for the frozen-thawed cycle group; this difference was statistically significant. In addition, the fresh ET cycles had the highest risk of EP, followed by day-3 embryo FET cycles; blastocyst FET cycles had the lowest risk of EP, and the differences were all statistically significant.
  
  
  CONCLUSIONS
  Frozen-thawed ET cycles were associated with a statistically significantly lower risk of EP when compared with fresh cycles. These findings are consistent with ovarian stimulation being associated with an increased risk of EP.
authors.affiliation: Reproductive Medicine Center, Tongji Hospital, Tongji Medicine College, Huazhong University of Science and Technology, Wuhan, People's Republic of China.
authors.forename: Bo
authors.initials: B
authors.lastname: Huang
authors.affiliation: Reproductive Medicine Center, Tongji Hospital, Tongji Medicine College, Huazhong University of Science and Technology, Wuhan, People's Republic of China.
authors.forename: Dan
authors.initials: D
authors.lastname: Hu
authors.affiliation: Reproductive Medicine Center, Tongji Hospital, Tongji Medicine College, Huazhong University of Science and Technology, Wuhan, People's Republic of China.
authors.forename: Kun
authors.initials: K
authors.lastname: Qian
authors.affiliation: Reproductive Medicine Center, Tongji Hospital, Tongji Medicine College, Huazhong University of Science and Technology, Wuhan, People's Republic of China.
authors.forename: Jihui
authors.initials: J
authors.lastname: Ai
authors.affiliation: Reproductive Medicine Center, Tongji Hospital, Tongji Medicine College, Huazhong University of Science and Technology, Wuhan, People's Republic of China.
authors.forename: Yufeng
authors.initials: Y
authors.lastname: Li
authors.affiliation: Reproductive Medicine Center, Tongji Hospital, Tongji Medicine College, Huazhong University of Science and Technology, Wuhan, People's Republic of China.
authors.forename: Lei
authors.initials: L
authors.lastname: Jin
authors.affiliation: Reproductive Medicine Center, Tongji Hospital, Tongji Medicine College, Huazhong University of Science and Technology, Wuhan, People's Republic of China.
authors.forename: Guijin
authors.initials: G
authors.lastname: Zhu
authors.affiliation: Reproductive Medicine Center, Tongji Hospital, Tongji Medicine College, Huazhong University of Science and Technology, Wuhan, People's Republic of China. Electronic address: hamwond@gmail.com.
authors.forename: Hanwang
authors.initials: H
authors.lastname: Zhang
mesh_terms: D000328:Adult; D002681:China / Q000453:epidemiology; D015925:Cryopreservation / Q000706:statistics & numerical data*; D004624:Embryo Transfer / Q000706:statistics & numerical data*; D004622:Embryo, Mammalian; D005260:Female; D005307:Fertilization in Vitro / Q000706:statistics & numerical data; D006801:Humans; D015994:Incidence; D007246:Infertility / Q000453:epidemiology* / Q000628:therapy*; D008875:Middle Aged; D010062:Ovulation Induction / Q000706:statistics & numerical data; D011247:Pregnancy; D011256:Pregnancy Outcome / Q000453:epidemiology*; D011271:Pregnancy, Ectopic / Q000453:epidemiology*; D012189:Retrospective Studies; D018570:Risk Assessment; D016896:Treatment Outcome; D055815:Young Adult
keywords: Ectopic pregnancy; embryo cryopreservation; fresh cycle; frozen-thawed ET; ovarian stimulation