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

Implantation after embryo transfer is considered a major obstadein terms of pregnancy rates after in-vitro fertilization. Aflexible approach to the date of replacement, based on the factthat the most suitable embryonic structure for proper implantationis the four- to eight-cell embryo, has been studied. One-hundred-and-twentypatients with various aetiologies of infertility were stimulatedwith HMG or combined HMG and FSH, then treated by three differentmethods of embryo replacement. In group I embryos were replacedin mothers 48 h after ovum retrieval; in group II replacementswere carried out 72 h after retrieval; and in group III replacementswere related to embryonic cleavage development. Mean levelsof oestradiol when HCG was given averaged 1301 ± 121pg/ml, 1016 ± 96 pg/ml and 1182 ± 101 pg/ml inthe three groups, respectively. There was no significant differencein the average number of embryos transferred among the variousgroups. The pregnancy rates per transfer were 21.8, 24.2 and38.7%, respectively (P < 0.001). Although more investigationis required, a dynamic approach to embryo replacement mightsignificantly improve pregnancy rates, because of improved interactionsbetween the embryos and the uterus.