Women's Health

Methods

Development of cardiovascular amplitude metric from continuous wearable data

Key Findings

• HRV varies predictably across menstrual cycle phases
• Cardiovascular amplitude correlates with hormonal changes
• Irregular cycles associated with higher cardiovascular disease risk
• Non-invasive monitoring of female physiology possible

Limitations

New metric requires further validation

Methods

Continuous monitoring of HR and HRV circadian rhythms during pregnancy

Key Findings

• Autonomic nervous system regulates pregnancy adaptations
• HR and HRV circadian patterns change during pregnancy
• Circadian rhythm parameters may predict complications
• Non-invasive biomarker potential for maternal health

Limitations

Further research needed on complication prediction

Methods

Multimodal smart ring worn from 30 weeks gestation until delivery

Key Findings

• Autonomic activity reflects neuroendocrine changes before labor
• Transition from pregnancy to labor may be measurable via HRV
• Current due date estimates don't capture physiological factors
• Wearable data collection feasible throughout late pregnancy

Limitations

Research ongoing, predictive accuracy not yet established

Methods

Real-time wearable monitoring across multiple menstrual cycles

Key Findings

• SDNN, RMSSD, and HF power decrease during early luteal phase
• Lowest HRV approximately one week before menses
• HRV peaks about one week after menstruation ends
• Progesterone significantly predicts lower HRV within individuals
• Estrogen enhances parasympathetic activity post-menses

Limitations

Individual variation significant, cycle length varies

Methods

6-month HRT intervention study with pre/post HRV assessment

Key Findings

• SDNN increased from 28.8 to 35.4 ms after 6 months
• HF component (parasympathetic) significantly increased
• LF/HF ratio decreased, indicating better autonomic balance
• Effects may explain cardioprotective benefits of HRT
• Progestogen type may influence outcomes

Limitations

Timing of HRT initiation matters for cardiovascular effects

Methods

Apple Women's Health Study with continuous wearable monitoring

Key Findings

• HRV decreased from 39.9ms pre-pregnancy to 29.9ms in third trimester
• Heart rate increased significantly in second trimester
• HRV began rebounding in last weeks of pregnancy
• Circadian HRV patterns also change during pregnancy
• Altered HRV may predict pregnancy complications

Limitations

Normal variation significant, individual baselines matter

Methods

Comparison studies of HRV in OCP users vs non-users

Key Findings

• OCP users may have higher HRV during inactive (placebo) phase
• Natural menstrual cycle HRV variation may be blunted
• Different formulations may have different effects
• Exercise autonomic responses may be altered
• Overall effects appear modest in healthy women

Limitations

Mixed findings, many contraceptive formulations exist

Methods

HRV monitoring during and between hot flash episodes

Key Findings

• HRV decreases acutely during hot flash episodes
• Sympathetic activity increases, parasympathetic decreases
• Women with severe symptoms have lower baseline HRV
• Lower HRV may indicate increased cardiovascular risk
• Estrogen decline drives autonomic changes

Limitations

Individual symptom severity varies widely