Serum oestradiol and preovulatory follicular development before in-vitro fertilization

Twenty-three in-vitro fertilization (IVF) treatment cycles (four unstimulated and 19 clomiphene-stimulated) were assessed retrospectively to discern relationships among serum oestradiol (OE2) titre on the day that human chorionic gonadotrophin (hCG) was given and the number and size of ovulatory follicles available for aspiration of oocytes during laparoscopy 32-38 h after hCG injection. Since 12 of the cycles succeeded to the stage of embryo replacement and two normal term pregnancies resulted, the series as a whole offers a useful referent data base. When only one ovulatory follicle developed (n = 8) the average volume of aspirated follicular fluid was approximately 6 ml, equivalent to a follicular diameter between 22 and 23 mm. When multiple follicles developed (mean 2.7/patient, n = 15), average fluid volume/follicle was not significantly different, averaging approximately 5.5 ml. Serum OE2 titre on the morning before hCG was injected ranged between 0.9 and 5.5 nmol/l and corresponded to the number of follicles aspirated at laparoscopy. There was a highly significant linear correlation (r = 0.85, P less than 0.001) between this OE2 value (X nmol/l) and total aspirated fluid volume (Y ml) where Y = 2.07 + 3.65 X. Thus taking 6 ml as the 'typical' fluid volume, the calibration line and its 95% confidence limits could be used to establish provisional 'ideal' pre-hCG serum OE2 titre ranges corresponding to the development of one, two or three mature ovulatory follicles. This information, combined with a knowledge of the number of presumptive preovulatory follicles present (assessed by ovarian ultrasound), can aid the timing of the hCG injection before IVF.