Serum follicle-stimulating hormone inhibition is a marker for preovulatory oocytes in in-vitro fertilization and embryo transfer.

A retrospective analysis was performed on 64 cycles stimulated with human menopausal gonadotrophin and/or pure follicle-stimulating hormone (FSH) and oestrogen (E2) levels. The increase in serum E2 on the day of HCG administration did not correlate (r = 0.05) with the number of preovulatory oocytes (preovs) or with an increase or decrease in serum FSH (r = 0.31). However, the change in serum FSH showed a significant correlation with the number of preovs (r = -0.95, P = 0.013). The probability of obtaining two or more preovs was relatively greater (1.47x) than that of other IVF patients, when there was a drop in FSH of 5% on the day of human chorionic gonadotrophin administration.