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

It has been suggested that seasonal variation in endometrialreceptivity may occur in women, which could affect the likelysuccess of in-vitro fertilization (IVF) treatment. We thereforestudied implantation rates (fetal sacs as a proportion of embryostransferred) as an indirect index of receptivity in a narrowlydefined population of women under 40 years old with normal ovulatorycycles and normal uterus and men with normal sperm function.A total of 577 cycles of IVF treatment were undertaken usinga standard protocol of pituitary desensitization and ovarianstimulation during the 3 years 1990–1992. Results werecompared between calendar months and 3-month seasons. The overallimplantation rate was 14.9% of embryos, and the clinical pregnancyrate was 30.3% of cycles reaching egg collection. There wereno significant differences in the monthly rates of eggs collected,fertilization and cleavage, or embryos transferred. Implantationrates varied to a greater extent but analysis of variance showedno seasonal variation. These findings do not support a seasonalvariation in ovarian responsiveness or endometrial receptivitywhen stimulated for IVF treatment, but larger studies are neededfor firm conclusions to be drawn.