Background. Altitude tolerance and acute mountain sickness (AMS) susceptibility in women remains insufficiently understood. One reason is the lack of a simple approach to monitoring sexual hormones and their influence on AMS. This pilot study aimed to investigate AMS incidence and the feasibility to self-monitor female sexual hormones at altitude.

Methods. This prospective pilot study was conducted in healthy, non-smoking, premenopausal women aged 19-28y, and residing <1000m. Participants underwent baseline evaluations at 760m and traveled to 3100m or 3600m for 2 days/nights. AMS was regularly assessed using Lake Louise score, including headache, vital signs, and pulse oximetry. Participants monitored oestrogen, progesterone, and luteinizing hormone using the proov device for 30 days.

Results. Overall, 1159 of 1230(94%) urinary hormone assessments were successful. At 3100m, 10 of 21(48%) women (mean±SD age 23.1±2.3y, BMI 22.7±3.3kg/m2) were diagnosed with AMS, SpO2 was 93.0±1.6%, LLS 2.0±1.9. At 3600m, 14 of 20(70%) women had AMS (age 23.8±2.6y, BMI 22.8±3.5kg/m2), SpO2 was 86.7±2.9% (P<0.05 vs. 3100m), LLS was 3.0±2.3 (P=0.163 vs. 3100m). Severe AMS (LLS >4 points) was 9% and 20% (P=0.400 between altitudes). Regression analysis showed a negative correlation between SpO2 and LLS (coef.[95%CI], of -0.2[-0.3;-0.0], P=0.030).

Conclusion. This pilot study showed good adherence and feasibility of monitoring female sexual hormones. Premenopausal women showed a higher AMS incidence at 3100m and 3600m compared to incidence rates in men. Despite the association of AMS severity with hypoxemia, severe AMS remained comparable between altitudes. These results lay the ground for large prospective cohort studies in women traveling to high altitudes.