Comparison of two ovulation tests to predict timing of the late follicular phase for menstrual cycle research in premenopausal females.

Menstrual cycle peak estradiol occurs in the late follicular (LF) phase just prior to the luteinizing hormone (LH) surge and ovulation. Therefore, to examine the impact of menstrual cycle estradiol fluctuations, it is desirable to perform assessments closely prior to ovulation. Standard ovulation tests (SOT) identify the LH surge and confirm that ovulation occurred after LF testing. Advanced ovulation tests (AOT) detect a rise in estrogen before the LH surge. We hypothesized that using the AOT to schedule LF testing between the rise in estradiol and LH surge would decrease the LF visit:ovulation interval vs. the SOT. Twenty-one naturally menstruating females (22 ± 4 years) participated in an early follicular (EF) and LF visit. The LF visit scheduling employed an AOT (n = 10) or SOT (n = 11). There was no difference in the LF visit:ovulation interval between tests (AOT = 2.7 ± 2.2 days, SOT = 2.5 ± 1.7 days; p = 0.859). Estradiol increased from the EF to LF phase, regardless of the ovulation test used (phase p < 0.001, test p = 0.528, interaction p = 0.099), and Δestradiol was negatively correlated with LF visit:ovulation interval (r = -0.454, p = 0.050). In this preliminary study, the AOT estrogen signal did not support scheduling the LF visit closer to ovulation or during higher estradiol vs. the SOT. Future studies should explore different methods to identify the menstrual cycle estradiol peak.