Objective: To determine strictly comparable rates per embryo of implantation and birth of a baby related to the woman's age, which would be representative of natural fertility at least in relative terms.
Design: Comparative study of IVF-ET results controlling for confounding variables including cause and duration of infertility, history of previous pregnancy, hormonal treatment, rank cycle of treatment, and numbers of embryos transferred and available.
Setting: University comprehensive fertility service.
Patients: All couples (n = 561) in their first cycle of treatment reaching oocyte collection, women with normal uterus and ovulatory cycles, and men with normal sperm.
Interventions: Standardized methods of pituitary desensitization, ovarian stimulation, and IVF-ET, and maximum of three embryos transferred.
Main outcome measures: Oocytes, pregnancies, and live births per cycle; fertilization and cleavage rates; embryo implantation and live baby rates.
Results: The numbers of oocytes and consequent embryos declined with age but fertilization and cleavage rates rose slightly. Embryo implantation rates were reduced when no more than three embryos were available (9.3 percent), especially in women aged 35 to 39 years (6.2 percent) or older compared with four or more embryos (17.1 percent) but were equally low in all women over 40 years even with more embryos (6.1 percent). In the age bands 25 to 29, 30 to 34, 35 to 39, and 40 to 44 years, the rates per embryo of implantation were 18.2 percent, 16.1 percent, 15.3 percent, and 6.1 percent, respectively, and of a live baby were 15.7 percent, 12.1 percent, 12.0 percent, and 3.5 percent.
Conclusions: Embryo implanting ability and survival decline gradually after 30 years of age, but by more than two thirds after 40 years and in younger women with reduced ovarian capacity.