The four stages of the menstrual cycle form the basis of a woman’s life, and living in tune with them can help master fertility, energy levels, and mood.
The cycle has important ramifications for a woman’s health, lifestyle, and career. When you know how to interpret your body’s cues, you can make informed decisions about reproductive health, fitness, and productivity. What’s more, understanding the menstrual cycle can decode the onset of menopause, or conditions such as PCOS, endometriosis, or even cancers.
Highlights
- The four phases of the menstrual cycle are the menstrual, follicular, ovulation, and luteal stages.
- Each stage brings fluctuations in mood, well-being, energy levels, and fertility.
- Tracking the cycle using biometric wearables can improve accuracy – especially for women with irregular cycles.
How you might feel at each stage of the cycle
The menstrual cycle is a natural process in the female reproductive system, preparing the body for pregnancy each month. It’s regulated by hormones and typically spans 28 days — although it can range anywhere from 21 to 35 days.
The cycle unfolds in four main phases:
Menstrual Phase (Typically Days 1–5)
Day one of the menstrual cycle occurs when bleeding begins. The body sheds the uterine lining because pregnancy hasn’t occurred, and the brain signals the ovaries to start preparing for a new cycle.
How you might feel: Tired, low on energy, or moody. Cramping, bloating, and discomfort are common.
Follicular Phase (Typically Days 1–13)
The beginning of the follicular phase overlaps with the menstrual phase as the body starts producing increasing levels of estrogen. Around the end of this phase, the body produces a hormone called LH (luteinizing hormone), which prepares the body for ovulation.
How you might feel: More energetic, social, and optimistic as estrogen levels rise.
Ovulation Phase (Approximately day 14)
This is when the ovary releases an egg, making it the most fertile high point of the cycle. A spike in LH triggers ovulation, and the egg travels into the fallopian tube.
How you might feel: At your best — confident, energetic, and possibly with a higher libido. Some may notice mild bloating or slight pelvic discomfort to one side, which is traditionally called mittelschmerz.
Luteal Phase (Days 15–28)
After ovulation, the empty follicle turns into the corpus luteum, which produces progesterone to maintain the uterine lining, preparing for the possibility of the egg having been fertilized. If pregnancy doesn’t occur, progesterone levels drop, triggering your next period.
How you might feel: More tired, increased body temperature, emotionally vulnerable, or irritable as progesterone rises. You may also experience bloating, cravings or breast tenderness leading up to your period.
Each phase is influenced by hormone fluctuations, and understanding them can provide insights into not just fertility but also overall health, mood, and energy levels.
How to track the four stages of the menstrual cycle
When it comes to tracking your menstrual cycle and related biomarkers, there are several options ranging from highly accurate, clinically accepted methods to more accessible yet less reliable alternatives.
The gold standard for tracking is ovarian sonography via a transvaginal ultrasound. Hormonal profiling through blood tests is another gold-standard method, offering an in-depth look at levels of estrogen, progesterone, and luteinizing hormone to confirm ovulation and detect hormonal imbalances. However, both of these are invasive, expensive and based in clinical settings. They also can’t be done continuously and offer a snapshot of the body’s state. A spin-off of blood hormone testing is the urine-based tests that check metabolites of the major hormones (estrogen, progesterone, and LH) in the urine.
Tracking basal body temperature (BBT), using a specialized BBT thermometer, is a low-cost, non-invasive option. It links the rise in body temperature with increased progesterone levels. However, it requires daily consistency and is sensitive to external factors such as sleep patterns or illness. Taking a reading at the same time early in the morning is also inconvenient.
Calendar methods or urine-based ovulation predictor kits are simple and effective but are not well suited to women with an irregular cycle.
Wearable devices, such as the Ultrahuman Ring AIR, can track the menstrual cycle using biometrics. Biomarkers such as skin temperature, heart rate, and heart rate variability (HRV) provide continuous, at-home monitoring, making them less invasive than clinical methods like sonography or blood tests and more effective at tracking irregular cycles.
An Ultrahuman study of its Cycle and Ovulation PowerPlug found that its algorithm was closely aligned with gold-standard hormone tests.
Menstrual cycle, heart rate, and HRV decoded
Your body gives subtle signs throughout the menstrual cycle. By keeping track of biomarkers like skin temperature, resting heart rate (RHR), and heart rate variability (HRV), you can gain insights into how these markers behave during your cycle and take action toward better health.
These changes, driven mainly by estrogen and progesterone, provide clues about metabolism, stress levels, and overall well-being.
For example, research shows that after ovulation, skin temperature rises, RHR tends to go up during the luteal phase, and HRV drops. Knowing these patterns can help recognize when the body might need more rest or when it’s time to push.
Data from over 4,055 menstrual cycles revealed some predictable patterns:
- Skin temperature rises post-ovulation.
- RHR climbs during the luteal phase.
- HRV drops.
These patterns help identify when the body might be more stressed, in need of rest, or primed for a rigorous workout.
How your vitals change in each phase of the menstrual cycle
- Menstrual Phase (Typically Day 1): As hormone levels drop significantly, both skin temperature and RHR decrease, signaling the start of your period. HRV starts to rise, indicating a transition back to a more balanced state.
- Follicular Phase (Typically Days 1–14): Biomarkers like skin temperature and RHR remain steady. HRV stays high, reflecting a state of recovery and balance.
- Ovulation (Approximately Day 14): As estrogen peaks, biomarkers start to shift. HRV remains high, and this is typically when you feel at your best with high energy levels. Skin temperature rises slightly due to increased progesterone.
- Luteal Phase (Typically Days 15–28): After ovulation, progesterone increases, which results in higher skin temperature (around 0.5°C) and resting heart rate (around 3–5 bpm). You might notice your body feels warmer. However, HRV tends to drop, indicating more stress on the body.
Conclusion
Understanding the menstrual cycle is not only essential for fertility and planning, but it can also offer a window into how we feel and perform.
Tracking the cycle has previously meant using invasive testing or imprecise calendar solutions that are inflexible for women with changeable or irregular cycles.
