Apparent lack of seasonal variation in implantation rates after in-vitro fertilization.

It has been suggested that seasonal variation in endometrial receptivity may occur in women, which could affect the likely success of in-vitro fertilization (IVF) treatment. We therefore studied implantation rates (fetal sacs as a proportion of embryos transferred) as an indirect index of receptivity in a narrowly defined population of women under 40 years old with normal ovulatory cycles and normal uterus and men with normal sperm function. A total of 577 cycles of IVF treatment were undertaken using a standard protocol of pituitary desensitization and ovarian stimulation during the 3 years 1990-1992. Results were compared between calendar months and 3-month seasons. The overall implantation rate was 14.9% of embryos, and the clinical pregnancy rate was 30.3% of cycles reaching egg collection. There were no significant differences in the monthly rates of eggs collected, fertilization and cleavage, or embryos transferred. Implantation rates varied to a greater extent but analysis of variance showed no seasonal variation. These findings do not support a seasonal variation in ovarian responsiveness or endometrial receptivity when stimulated for IVF treatment, but larger studies are needed for firm conclusions to be drawn.