Trophectoderm biopsy in human blastocysts.

Trophectoderm biopsy was carried out on 47 human blastocysts. A slit was made in the zona pellucida opposite the inner cell mass by micromanipulative techniques. The human blastocyst zona offered more resistance to slitting compared to that of the mouse. After 18-24 h, controlled herniation of the trophectoderm cells was observed. These cells were biopsied when the diameter of the herniation was approximately equal to that of the blastocyst. The size of the slit and the stage of embryonic development at which slitting was performed were important for successful herniation to occur. After slitting, 76% of day 5-6 blastocysts showed herniation whilst only 42% of day 7-8 blastocysts herniated. Further development of the manipulated embryos was not apparently impaired, as hatching occurred in 44% of the former and 20% of the latter, compared with 18.1% in non-manipulated controls. The biopsied cells (approximately 10-30) usually remained in a clump but 14% formed vesicles on the day after biopsy. There was, however, no evidence of adherence to the dish or formation of monolayers. These results demonstrate the feasibility of trophectoderm biopsy in human blastocysts and that sufficient extra-embryonic material can be obtained by this technique for preimplantation diagnosis of genetic disorders.