Received April 23, 1999
Accepted October 16, 1999

The use of GnRH analogues represents one of the most important advances in assisted reproductive programs. GnRHa in combination with menotropins or recombinant FSH to induce folliculogenesis for controlled ovarian hyperstimulation in women undergoing IVF has raised pregnancy rates. The benefits from its use derive principally from the absence or reduction in the incidence of premature LH surge and premature luteinization as a consequence of pituitary down-regulation. The most widely used regimen is the long protocol due to its better results, hence it is important to confirm pituitary suppression before starting superovulation. Classically down regulation is confirmed by the measurement of serum oestradiol. ln this study we evaluated 268 patients performing IVF treatment, using long protocol regimen. Endometrial thickness measurement was performed in the same day of E2 analysis in order to evaluate whether it can be an isolated diagnostic tooI for pituitary down-regulation. We found a positive correlation of 92.9% between the E2 leveis and the endometrial thickness measured by ultrasound. This results shows the importance of this method to predict the pituitary suppression in IVF cycles.