Advanced embryo development during extended in vitro culture: observations of formation and hatching patterns in...

Human embryos not chosen for fresh transfer or cryopreservation were maintained in extended in vitro culture for up to 9 days after fertilization to observe blastocyst formation and hatching features. These non-transferred embryos were derived from 64 consecutive IVF cycles, and were not cryopreserved either because of compromised morphology or because the patients did not consent to cryopreservation for personal reasons. Embryos were cultured individually to monitor daily growth until developmental arrest, and differential blastocyst formation and hatching were analysed among groups of patients and embryos. In the population studied, hatching occurred most commonly on day 7 after fertilization (range 5-9 days). A total of 301 blastocysts was observed, of which 116 (38.5%) eventually hatched in vitro irrespective of day of formation. A trend towards earlier blastocyst formation and a greater likelihood of hatching was noted in this population. Both blastocyst formation and hatching appeared negatively correlated with increasing maternal age and higher basal serum FSH concentrations on day 3 of development, although these trends did not reach statistical significance. Comparison of intracytoplasmic sperm injection (ICSI) (n = 25) and conventional insemination (n = 39) cycles showed a similar rate of blastocyst formation in both groups (54 and 52%, respectively; P > 0.05), but hatching patterns varied significantly between these groups (4.1 versus 61.6%, respectively; P < 0.0001). The discovery of marked impairment of hatching among non-transferred ICSI embryos supports the case for reconsideration of the appropriateness of assisted blastocyst hatching in selected cases.