During ovarian stimulation for IVF, clinicians are constantly balancing two priorities: encouraging a strong follicular response while maintaining safety and optimising outcomes. Ultrasound provides critical structural information, but it is hormones — particularly estradiol (E2) — that reveal how actively the ovaries are responding at a biological level.
Recent evidence highlights that it is not just the absolute estradiol value that matters, but how estradiol levels change over time during stimulation.
Estradiol is produced by granulosa cells within developing follicles. As follicle number and activity increase, circulating E2 levels rise accordingly. For decades, clinicians have used estradiol measurements to support dose adjustments, guide trigger timing, and reduce the risk of excessive ovarian response.
What is becoming increasingly clear is that the trajectory of estradiol rise — rather than a single snapshot — provides meaningful insight into treatment response.
A large 2025 study published in Scientific Reports analysed almost 9,400 first-time IVF/ICSI cycles and examined relative changes in estradiol during controlled ovarian stimulation rather than absolute thresholds alone. The findings showed that patients with greater proportional increases in estradiol during stimulation had significantly higher blastocyst formation rates, clinical pregnancy rates, and live birth rates compared with lower estradiol response groups.¹
Importantly, the authors found no single estradiol “cut-off” that predicted success. Instead, outcomes tracked with how effectively estradiol levels rose in response to stimulation — reinforcing estradiol as a dynamic marker of ovarian responsiveness.
Relative estradiol changes capture several clinically relevant factors at once:
Follicular activity, not just follicle count
Biological responsiveness to gonadotropins
Early signals of sub-optimal or excessive response
Two patients may have similar estradiol values on a given day, but very different trajectories leading up to that point. Monitoring trends helps clinicians recognise these differences earlier and respond appropriately.
This approach aligns well with modern IVF practice, which increasingly focuses on individualised stimulation strategies rather than fixed protocols.
Regular hormone monitoring during stimulation allows clinicians to:
Fine-tune gonadotropin dosing
Optimise trigger timing
Identify atypical endocrine patterns
Reduce the risk of complications such as OHSS
The emerging evidence suggests that paying attention to estradiol patterns — not just peak values — may also support better prediction of downstream outcomes such as blastocyst development and live birth.
As IVF continues to evolve toward more personalised care, hormone monitoring remains a cornerstone of informed decision-making. Studies like the 2025 Scientific Reports analysis reinforce the value of serial estradiol measurements and highlight how relative hormonal changes can provide actionable insight well before retrieval day.
Estradiol monitoring is therefore not simply about checking a number — it is about understanding how each patient’s ovaries are responding in real time, and using that information to support safer, more effective treatment. Cyclic ProDX deliver estradiol results into the hands of clinicians within 30 minutes of phlebotomy.
Huang, W., Wei, L., Tang, J. et al. Impact of relative estradiol changes during ovarian stimulation on blastocyst formation and live birth in assisted reproductive technology. Sci Rep 15, 15617 (2025). https://doi.org/10.1038/s41598-025-00200-5