Hatching of in vitro fertilized human embryos is influenced by fertilization method

Objective: To describe hatching of human embryos and investigate differences in hatching between IVF and intracytoplasmic sperm injection (ICSI)-fertilized embryos with the use of time-lapse monitoring. Design: Clinical observational study. Setting: University-based fertility clinic. Patient(s): From February 2011 to July 2012, 161 women consented to embryo culture in a time-lapse incubator until day 6 after oocyte retrieval. The mechanism of hatching was recorded and related to method of fertilization (ICSI or IVF) and clinical pregnancy outcome. Intervention(s): IVF or ICSI. Main Outcome Measure(s): Hatching pattern. Result(s): A total of 430 IVF fertilized embryos from 62 patients and 594 ICSI-fertilized embryos from 99 patients were included. We observed spontanous hatching in 165 IVF embryos and 215 ICSI embryos. Two distinct mechanisms of hatching were observed. Type 1 was characterized by penetration of the zona pellucida (ZP) by small trophectoderm projections, whereas type 2 was preceded by a regular rupture of the ZP followed by extrusion of the blastocyst. Type of hatching was significantly different between IVF and ICSI embryos, with type 2 observed more often in IVF embryos than in ICSI embryos. Furthermore, IVF embryos escaped the ZP more readily than ICSI embryos. Regardless of the type of hatching, implantation rates were similar. Conclusion(s): We describe two distinct mechanisms of in vitro hatching related to fertilization method and suggest that hatching pattern is associated with fertilization method. The hatching pattern has, however, no influence on future implantation. (C)2013 by American Society for Reproductive Medicine.