title: [Association of fertilization strategy and embryo transfer time with the incidence of ectopic pregnancy].
abstract: OBJECTIVE
  To investigate the correlation of the fertilization strategy and embryo transfer (ET) time with the incidence of ectopic pregnancy.
  
  
  METHODS
  We selected 3,331 fresh and 2,706 frozen-thawed ET cycles for the patients undergoing in vitro fertilization (IVF) and intracytoplasmic sperm injection (ICSI). The fresh transfers included 2 546 IVF-ET and 785 ICSI-ET cycles and 2,220 day-3 embryo and 1,111 day-5 blastocyst transfers, while the frozen-thawed transfers included 2,080 IVF-ET and 626 ICSI-ET cycles and 741 day-3 embryo and 1 965 day-5 or -6 blastocyst transfers. We compared the incidence rate of ectopic pregnancy associated with different fertilization strategies and ET time.
  
  
  RESULTS
  The incidence rate of ectopic pregnancy was 1. 41% (36/2 546) in the IVF-ET cycles and 3.44% (27/785) in the ICSI-ET cycles of the fresh transfers, significantly lower in the IVF-ET than in the ICSI-ET cycles (P < 0.01), and it was 1.01% (21/2,080) in the IVF-ET cycles and 0.80% (5/626) in the ICSI-ET cycles of the frozen-thawed transfers, with no remarkable difference between the two groups (P > 0.05). The IVF-ET and ICSI-ET cycles included 2,220 fresh day-3 (F-D3) embryos, 1,111 F-D5 blastocysts, 741 frozen-thawed day-3 (T-D3) embryos, and 1,965 T-D5/6 blastocysts. The incidence rate of ectopic pregnancy was 1.71% (n = 38) in the F-D3, 2.25% (n = 25) in the F-D5, 1.35% (n = 10) in the T-D3, and 0.81% (n = 16) in the T-D5/6 group, respectively, significantly lower in the T-D5/6 than in the other three groups (P < 0.05).
  
  
  CONCLUSIONS
  The incidence rate of ectopic pregnancy is associated with fertilization strategies, which is significantly lower in frozen-thawed than in fresh embryo transfers.
authors.forename: Ming-zhao
authors.initials: MZ
authors.lastname: Li
authors.forename: Wan-qiu
authors.initials: WQ
authors.lastname: Zhao
authors.forename: An-qi
authors.initials: AQ
authors.lastname: Ren
authors.forename: Juan-zi
authors.initials: JZ
authors.lastname: Shi
mesh_terms: D001755:Blastocyst; D004624:Embryo Transfer / Q000009:adverse effects / Q000379:methods* / Q000706:statistics & numerical data; D005260:Female; D005307:Fertilization in Vitro / Q000009:adverse effects / Q000379:methods* / Q000706:statistics & numerical data; D006801:Humans; D015994:Incidence; D011247:Pregnancy; D018873:Pregnancy Rate; D011271:Pregnancy, Ectopic / Q000453:epidemiology* / Q000209:etiology; D020554:Sperm Injections, Intracytoplasmic / Q000009:adverse effects / Q000379:methods / Q000706:statistics & numerical data