title: A randomized double-blind controlled study of the efficacy of laser-assisted hatching on implantation and pregnancy rates of frozen-thawed embryo transfer at the cleavage stage.
abstract: BACKGROUND
  Assisted hatching (AH) in fresh embryo transfer (ET) cycles increases the implantation and pregnancy rates, especially in women with a poor prognosis, repeated implantation failures and in older women. Little information exists in the literature regarding the role of AH in frozen-thawed embryo transfer (FET) cycles.
  
  
  METHODS
  Embryos were cryopreserved at the cleavage stage. On the day of FET, 160 patients were randomized according to a computer-generated randomization list in sealed envelopes into the AH group and the control group. The patients and the clinicians were blinded to the group assigned. In the AH group, the outer half of the zona pellucida over a quarter of the diameter of zona was removed using a 1480 nm non-contact laser.
  
  
  RESULTS
  The two groups were comparable in terms of demographic characteristics, ovarian response of the stimulated cycle and quality of fresh and frozen-thawed embryos. No differences in implantation, pregnancy and multiple pregnancy rates were found between the two groups. There was a non-significant trend of a higher implantation rate in the AH group when the zona thickness was > or = 16 mm.
  
  
  CONCLUSIONS
  Laser AH did not improve the implantation rate of FET cycles and should not be performed routinely in all frozen-thawed embryos at the cleavage stage.
authors.affiliation: Department of Obstetrics and Gynaecology, The University of Hong Kong, Hong Kong Special Administrative Region, People's Republic of China. nghye@hkucc.hku.hk
authors.forename: Ernest Hung Yu
authors.initials: EH
authors.lastname: Ng
authors.forename: Fatima
authors.initials: F
authors.lastname: Naveed
authors.forename: Estella Yee Lan
authors.initials: EY
authors.lastname: Lau
authors.forename: William Shu Biu
authors.initials: WS
authors.lastname: Yeung
authors.forename: Carina Chi Wai
authors.initials: CC
authors.lastname: Chan
authors.forename: Oi Shan
authors.initials: OS
authors.lastname: Tang
authors.forename: Pak Chung
authors.initials: PC
authors.lastname: Ho
mesh_terms: D000328:Adult; D002970:Cleavage Stage, Ovum; D015925:Cryopreservation / Q000379:methods*; D004311:Double-Blind Method; D010064:Embryo Implantation; D004624:Embryo Transfer; D005260:Female; D006801:Humans; D007834:Lasers; D011247:Pregnancy; D018873:Pregnancy Rate; D011446:Prospective Studies