[Human embryo cryopreservation].

Widespread incorporation of human embryo cryopreservation into in-vitro fertilization (IVF) programs may reduce the risk of multiple gestation and severe ovarian hyperstimulation syndrome while contributing to an overall increase in pregnancy rates. The main known complication arising from ovarian stimulation is ovarian hyperstimulation syndrome (OHSS). The development of severe OHSS is contingent on either exogenous administration of hCG or endogenous pregnancy-derived hCG stimulation. The rationale behind the strategy of electively cryopreserving all embryos from woman at risk of developing OHSS is therefore to avoid these additional influences of the exogenous and trophoblastic HCG upon the ovary. Successful implantation depends on embryo quality and uterine receptivity. If a good embryo was present, among those in the cleavage stage, the pregnancy rate was significantly higher (41.5%) after the transfer of embryos at the 3 approximately 4 cell stage in the cases of pronuclear-stage freezing. A significantly higher pregnancy rate of multilayered echogenic patterns was observed when pregnancy and nonpregnancy cycles were compared. No differences in mean endometrial thickness were observed when pregnancy and non pregnancy cycles were compared. No pregnancies occurred when endometrial thickness was less than 5 millimeters. A statistically significant decrease in pregnancy rate was seen when thawed embryo transfer is performed in a natural cycle in patients who were 35 to 39 years old. No age-related decline was seen in patients in which transfer was performed in the hormone replacement cycle.