title: An improved mechanical technique for assisted hatching.
abstract: BACKGROUND
  Varied clinical outcomes of assisted hatching (AH) have been reported. We attempt to investigate whether the size of the zona opening created by AH is adequate for blastocyst hatching, and, if not, set up a new method to improve it.
  
  
  METHODS
  A new AH technique, long zona dissection (LZD), was established, and experiments were performed to compare the effects of different sizes of zona opening on complete hatching of blastocysts in mouse and human embryos in vitro.
  
  
  RESULTS
  The LZD technique can create a long zona slit on early embryos, even blastocysts, with the slit size beyond two-thirds of zona diameter. Compared with three-dimensional partial zona dissection, LZD can significantly enhance the hatching speed and the rate of complete hatching of mouse blastocysts (93.9%). All (100%) human blastocysts completely hatched following LZD; however, when the slit size after AH was about two-fifths of zona diameter, more of the larger inner cell masses (ICM) became trapped by the zona opening during hatching than the smaller ICM (53.3 versus 12.5%, P = 0.01).
  
  
  CONCLUSIONS
  Zona opening of moderate size following AH is inadequate for the completion of blastocyst hatching in vitro; in some cases, however, it can be significantly improved by LZD.
authors.affiliation: National Laboratory of Medical Genetics of China, Central South University, Changsha, 410078, People's Republic of China.
authors.forename: Q F
authors.initials: QF
authors.lastname: Lyu
authors.forename: L Q
authors.initials: LQ
authors.lastname: Wu
authors.forename: Y P
authors.initials: YP
authors.lastname: Li
authors.forename: Q
authors.initials: Q
authors.lastname: Pan
authors.forename: D E
authors.initials: DE
authors.lastname: Liu
authors.forename: K
authors.initials: K
authors.lastname: Xia
authors.forename: D S
authors.initials: DS
authors.lastname: Liang
authors.forename: F
authors.initials: F
authors.lastname: Cai
authors.forename: Z G
authors.initials: ZG
authors.lastname: Long
authors.forename: H P
authors.initials: HP
authors.lastname: Dai
authors.forename: J H
authors.initials: JH
authors.lastname: Xia
mesh_terms: D000818:Animals; D001755:Blastocyst / Q000502:physiology; D046149:Embryo Culture Techniques / Q000379:methods*; D006801:Humans; D019563:Mechanics; D051379:Mice; D008815:Mice, Inbred Strains