Abstract Study question How effective and user-friendly is a non-invasive, patient-operated urine test (Kinder) in tracking reproductive hormone levels during ovarian stimulation (OS) treatment in an IVF cycle? Summary answer Urinary E1-3G correlates well with blood E2 levels and ovarian follicle development. Patients found it easy and stress-free to perform the urine test at home. What is known already Monitoring blood reproductive hormone levels during OS is a widely accepted practice to ensure the optimal ovarian response to gonadotropin treatment, timing of oocyte maturation triggering and mitigating hyperstimulation risk. However, conventional blood testing is invasive, necessitating patients to travel to clinics for blood sampling, adding to their overall burden. Previous studies have revealed a robust correlation between blood E2 levels, and its corresponding urinary metabolites E1-3G. Kinder is a portable device designed for quantifying urinary E1-3G, allowing patients to conduct tests in the privacy of their homes, and for many obviating the need to travel substantial distances for monitoring. Study design, size, duration This is a prospective, single-cohort, study of Caucasian patients (28-34 years), conducted at Fertility Specialists of Western Australia in Perth, Australia, where patients may travel vast distances for treatment. Twenty-five patients were enrolled from Aug 2022-Aug 2023, and performed home urine tests utilizing the Kinder device in parallel with clinic scheduled blood (ELISA) and ultrasound tests. The primary end point of the study was the correlation between urinary and blood reproductive hormone concentrations (E1-3G). Participants/materials, setting, methods Spearman and Pearson correlation coefficients (CC) and 95% confidence intervals were calculated for E1-3G and E2, and E1-3G/E2 and follicle development (total volume of ovarian follicles by ultrasound). To assess patient acceptability patient-reported outcomes (PRO) were assessed using the State Trait Anxiety Inventory (STAI) questionnaire. Further, patient-reported experiences (PRE) were evaluated through the System Usability Scale (SUS) questionnaire, along with assessing their likelihood to recommend Kinder to their friends or family undergoing IVF treatment. Main results and the role of chance Upon analysing 100 concurrent urine and blood samples from 25 patients, a robust correlation was found between E1-3G and E2 levels (Spearman CC: 0.818, 95% CI: 0.680-0.904; Pearson CC: 0.847, 95% CI: 0.712-0.939). Additionally, we observed a moderate correlation between E1-3G levels and ovarian volume (Spearman CC: 0.701, 95% CI: 0.556-0.805; Pearson CC: 0.670, 95% CI: 0.519-0.781, n = 72), resembled the correlation between E2 levels and ovarian volume (Spearman CC: 0.874, 95% CI: 0.804-0.920; Pearson CC: 0.849, 95% CI: 0.770-0.902, n = 75). PRE: 22 out of 23 patients who completed the survey confirmed that they would definitely, or probably, recommend Kinder. The mean SUS score (91.4) signified an excellent user experience. PRO: Anxiety levels were not affected by use of Kinder (STAI score below threshold of 42.38) in 18/20 patients who completed three STAI surveys (first one before and second one after the initial Kinder test; third one after the third/fourth Kinder test). Although 2/20 patients reported a STAI score of 49 in the final survey, suggesting increased anxiety, both affirmed in the PRE survey that they “will definitely recommend Kinder”, suggesting that the elevated STAI score can be attributed to the overall IVF treatment rather than the use of Kinder itself. Limitations, reasons for caution The sample size is relatively small, necessitating further multi-centre studies with a larger sample size to validate the findings. Wider implications of the findings The results suggest an acceptable interchangeability between at-home urine E1-3G and at-clinic blood E2 monitoring hormone levels during OS treatment. A digital health approach, combining tele-counselling, remote at-home hormone monitoring, and follicle tracking, could reduce patient burden and save many patients the inconvenience of travelling large distances for cycle monitoring. Trial registration number ACTRN12622000488707