Embryo viability associated with microassisted fertilization.

Embryo morphology and cleavage rates represent useful, but not absolute, measures of embryo viability. Oocyte and embryo chromosomal abnormalities affect embryo viability and are reflected to some degree in the morphology of oocytes and embryos. Microassisted fertilization techniques have been successfully used to treat severe male-factor infertility. Zona drilling using acidified Tyrode's solution is detrimental to oocyte and embryo viability and should not be used. Partial zona dissection (PZD) produces viable embryos that have developmental competence no different from that of routine IVF embryos, but the oocytes should be shrunken in hypertonic sucrose prior to PZD to avoid distortion and mechanical damage. The size of the cut in the zona pellucida is also critical and should be kept to a minimum to avoid loss of blastomeres during transfer. It appears from data on embryo quality, pregnancy rates and implantation rates that SUZI embryos have viability comparable to that of routine IVF embryos. Astonishingly, the passage of an injection needle directly into the ooplasm during ICSI has no effect on fertilization or developmental competence, as demonstrated by the excellent clinical pregnancy rates.