EStradiol and PRogesterone in In vitro ferTilization (ESPRIT): a multicenter study evaluating third- versus second-generation estradiol and progesterone immunoassays.

Purpose: To assess estradiol (E) and progesterone levels during ovarian stimulation determined by third-generation (Gen III) and second-generation (Gen II) Elecsys immunoassays.

Methods: E and progesterone concentrations were measured using Elecsys Gen III and Gen II immunoassays, and progesterone concentrations on the day of ovulation triggering were determined by LC-MS/MS. This was a retrospective, non-interventional study conducted at European tertiary referral infertility clinics in women aged 18-45 years, with a body mass index 18-35 kg/m, regular menses, and both ovaries.

Results: Serum samples were obtained from 230 women classified by oocyte retrieval as poor (33.0%; 0-3 oocytes), normal (40.9%; 4-15 oocytes), or high (26.1%; > 15 oocytes) responders. E and progesterone levels increased during ovarian stimulation, with greatest increases observed in high responders. Elecsys Gen III and Gen II assay results were highly correlated for E (Pearson's r = 0.99) and progesterone (r = 0.89); Gen III results were lower than Gen II for both E and progesterone. On the day of triggering, Gen III E and progesterone levels showed a difference of - 15.0% and - 27.9%, respectively. Progesterone levels (on day of triggering) measured by LC-MS/MS correlated better with Gen III (0.98) than Gen II (0.90). Mean relative differences for Gen III and Gen II assays versus LC-MS/MS were 14.6% and 62.8%, respectively.

Conclusion: E and progesterone levels determined with Elecsys Gen II and III assays were highly correlated; results were lower for Gen III versus Gen II. Differences observed for progesterone on the day of triggering may be clinically relevant.