Progression of excess embryos to the blastocyst stage predicts pregnancy and implantation rates after intracytoplasmic sperm injection.

Excess embryos from patients undergoing intracytoplasmic sperm injection and embryo transfer for male infertility were cultured to determine the rate and timing of their progression to the blastocyst stage. In 194 embryo transfer cycles, four embryos with the morphologically best grading were transferred and at least two embryos were cultured. The cycles were classified as: group 1: no excess embryos reached blastocyst stage, group 2: >50% of embryos reached blastocyst stage by days 4-5, group 3: <50% of embryos reached the blastocyst stage by days 4-5, group 4: >50% of the embryos reached blastocyst stage by days 6-7, group 5: <50% of the embryos reached blastocyst stage by days 6-7. All groups were similar regarding female age, duration of infertility, and parameters of ovarian stimulation. In group 1, clinical pregnancy and implantation rates were 14 and 11% respectively, and were similar to those of group 4. In group 2, clinical pregnancy and implantation rates were 75 and 33%. Multiple implantations occurred in 81% of group 2 or 3 cycles, compared to none in group 1 cycles. The results suggest that the development potential of the embryo is intrinsic, and that embryos which carry a high potential for development yield a high clinical pregnancy rate and multiple implantations.