Comparison of a fixed and dynamic protocol for embryo replacement in an IVF/ET programme.

Implantation after embryo transfer is considered a major obstacle in terms of pregnancy rates after in-vitro fertilization. A flexible approach to the date of replacement, based on the fact that the most suitable embryonic structure for proper implantation is the four- to eight-cell embryo, has been studied. One-hundred-and-twenty patients with various aetiologies of infertility were stimulated with HMG or combined HMG and FSH, then treated by three different methods of embryo replacement. In group I embryos were replaced in mothers 48 h after ovum retrieval; in group II replacements were carried out 72 h after retrieval; and in group III replacements were related to embryonic cleavage development. Mean levels of oestradiol when HCG was given averaged 1301 +/- 121 pg/ml, 1016 +/- 96 pg/ml and 1182 +/- 101 pg/ml in the three groups, respectively. There was no significant difference in the average number of embryos transferred among the various groups. The pregnancy rates per transfer were 21.8, 24.2 and 38.7%, respectively (P less than 0.001). Although more investigation is required, a dynamic approach to embryo replacement might significantly improve pregnancy rates, because of improved interactions between the embryos and the uterus.