Four Phases of the Menstrual Cycle: From Menstruation to Ovulation and Return

ENGLISH, Four Phases of the Menstrual Cycle: From Menstruation to Ovulation and Return

Introduction

Most couples don't know the names of their own cycle phases. Women talk about "that time" or "PMS," but not about what's happening biologically each day.

This is biology worth knowing.

Not because it's secret. But because when you understand what's happening in your body every day, all of natural family planning becomes clear. It's no longer a mystery. It's mathematics.

Arek always says: "You can't manage what you don't measure. You can't work with something you don't understand." The same is true of your cycle. When you know the phases, you know yourself.

Four Main Phases of the Menstrual Cycle

The average menstrual cycle lasts 28 days, but the normal range is 21 to 35 days. Your cycle may be different-and that's normal.

Phase 1: Menstruation (Days 1–5)

Other names: Menstrual phase, bleeding phase

This phase begins on the first day of visible bleeding.

What happens biologically:

• Oestradiol (oooestrogen) levels are lowest in the cycle
• Progesterone levels drop rapidly
• The lining of the uterus (endometrium), which was being prepared by progesterone, now breaks down and empties

What you feel:

• Bleeding, usually lasting 3–7 days
• Possible cramps (dysmenorrhea), especially on the first and second days
• Possible fatigue, mood depression, irritability (resulting from the sharp drop in hormones)
• Possible acne flare-up (if skin is reactive)

Significance for NFP:

• No cervical mucus (due to very low oestrogen)
• Low basal body temperature
• For couples avoiding pregnancy: menstruation is a time of complete abstinence in many NFP interpretations (due to possibility of infection and inability to observe mucus)
• For couples wanting pregnancy: menstruation is sometimes a quick time for relations, because there's no possibility of fertility

Advice: If you have menstrual pain, it may be caused by prostaglandins (natural substances that cause uterine contractions). Pain relievers like ibuprofen can help, but there are also natural methods-heat, massage, relaxation. Tracking your cycle helps you anticipate when pain may occur, allowing you to prepare.

Phase 2: Follicular Phase (Days 1–14)

Other names: Estrogen phase, rising phase

This phase begins on the first day of menstruation and ends at ovulation.

What happens biologically:

• The pituitary (a small gland in the brain) releases FSH (follicle-stimulating hormone)
• FSH stimulates the ovaries to produce follicles-fluid-filled sacs, each containing one immature egg
• As the follicle grows, it produces more and more oestradiol (ooestrogen)
• Estrogen stimulates the uterine lining to thicken and prepare for possible implantation
• Estrogen also affects cervical glands to produce more, increasingly clear mucus

What you feel:

• Increased energy (oestrogen has an energizing effect)
• Better mood, lower depression, higher motivation
• Increased sexual appetite (hormonally, and also due to the psychological effect of feeling good)
• Skin may be clearer and more radiant (oestrogen has an equalizing effect on collagen)

Significance for NFP:

• Basal body temperature is low
• Mucus begins to appear midway through the follicular phase
• First half of the follicular phase (days 1–7) is generally infertile for couples avoiding pregnancy, as long as mucus doesn't appear earlier

Advice: This is the best time for training, learning, creative projects. Oestrogen is highest in the follicular phase-this is when your brain works best. Use it.

Phase 3: Estrogen Peak and Ovulation (Days 12–16)

Other names: Periov ulatory phase, luteinizing hormone (LH) surge

This phase encompasses spectacular moments: the oestrogen peak, the LH peak, and ovulation itself.

What happens biologically:

• Usually two days before ovulation, oestrogen reaches its maximum level
• This high level of oestradiol sends a signal to the pituitary: "ENOUGH! Time for ovulation!"
• The pituitary responds with a rapid rise in LH (luteinizing hormone)
• This LH surge triggers ovulation within ~12–24 hours
• The follicle breaks, releases the mature egg, which begins its journey through the fallopian tube

What you feel:

• Peak sexual libido (this is the moment when nature wants you to reproduce)
• Possible mild pain in the area of the ovaries (mittelschmerz)-mild discomfort on one side of the abdomen
• Maximum cervical mucus flow-complete moisture, clarity
• Possible slight temperature dip just before ovulation (not all women experience this)

Significance for NFP:

• This is the living center of the fertile window
• For couples wanting pregnancy: best days for relations
• For couples avoiding pregnancy: complete abstinence
• Temperature may dip slightly just before ovulation, but usually rises within 24 hours

Note on LH detection: Some couples use LH surge detection tests (ovulation predictor kits). While FertilityFlow focuses on the three methods described in this guide (BBT, cervical mucus, and cycle awareness), LH testing can provide additional confirmation. For detailed guidance on LH-based methods, consult a certified NFP instructor.

Phase 4: Luteal Phase (Days 16–28)

Other names: Second-half phase, progesterone phase

This phase begins after ovulation and lasts until menstruation.

What happens biologically:

• After ovulation, the follicle cells that remained in the ovary transform into a structure called the corpus luteum (yellow body)
• The corpus luteum produces progesterone
• Progesterone maintains the uterine lining thick and rich with blood vessels-preparing for possible implantation
• If fertilization occurred, the embryo sends a signal of hCG hormone, which tells the corpus luteum: "Continue progesterone!" and pregnancy begins
• If fertilization didn't occur, the corpus luteum lives exactly 12–16 days, then dies, progesterone levels drop, and menstruation begins
• If fertilization didn't occur, the corpus luteum lives exactly 12–16 days, then dies, progesterone levels drop, and menstruation begins

What you feel:

• Possible PMS (premenstrual syndrome)-irritability, fatigue, mood changes, depression
• Possible changes in appetite-sometimes increased craving for sweets and fats (due to higher metabolic need in the luteal phase)
• Possible changes in libido-for some an increase, for some a decrease
• Bloating, breast tenderness, headaches on some days
• Possible noticeable swelling (water retention, caused by progesterone)

Significance for NFP:

• Basal body temperature is higher (~0.5°C) than in the follicular phase
• Mucus returns to being thick and dry within a few days of ovulation
• For couples avoiding pregnancy: the luteal phase (after the third day of elevated temperature) is completely infertile
• For couples wanting pregnancy: if pregnancy didn't occur, this is a time of waiting

Advice: PMS may be related to changes in neurotransmitters (especially serotonin) caused by progesterone, but the exact mechanisms are still being studied. Proper sleep, exercise, and magnesium can help. Also, when you know PMS is coming, you can schedule stressful conversations or important decisions for ANOTHER time-things that can be postponed.

Knowing the phases gives you control over your schedule.

Note on LH detection: Some couples use LH surge detection tests (ovulation predictor kits). While FertilityFlow focuses on the three methods described in this guide (BBT, cervical mucus, and cycle awareness), LH testing can provide additional confirmation. For detailed guidance on LH-based methods, consult a certified NFP instructor.

How These Phases Look on an NFP Chart

When you observe all three indicators (temperature, mucus, symptoms), the phases look like this:

PHASE 1 (Menstruation, Days 1–5)
- Temperature: low (~36.4°C)
- Mucus: absent
- Symptoms: bleeding, possible cramps
- NFP status: complete abstinence (many interpretations)

PHASE 2 (Rising Follicular, Days 6–10)
- Temperature: low (~36.4°C)
- Mucus: appears, begins to increase
- Symptoms: increasing energy, increasing sexual appetite
- NFP status: observe carefully, prepare for fertility

PHASE 3 (Periovu latory, Peak, Days 11–15)
- Temperature: dips, then rises rapidly
- Mucus: at peak, like egg white, maximum stretchiness
- Symptoms: peak libido, possible mittelschmerz
- NFP status: FERTILE-complete abstinence for couples avoiding pregnancy

PHASE 4 (Luteal, Days 16–28)
- Temperature: high (~36.9°C), stable
- Mucus: return to thickness, dry
- Symptoms: fatigue, possible PMS by end of cycle, breast sensitivity
- NFP status: INFERTILE (after third day of higher temperature)-relations are safe for couples avoiding pregnancy

Addressing Discomfort in Each Phase

Each phase has its own biology, and biology sometimes creates discomfort.

Menstruation, dysmenorrhea:

• Natural approach: heat, rest, gentle movement
• Anti-inflammatory: ibuprofen can reduce prostaglandins
• Long-term: tracking your cycle and lifestyle changes can help address dysmenorrhea

Follicular phase, usually the best:

• This is the time for projects, training, challenges
• If there is discomfort, it may be caused by stress or lack of sleep

Oestrogen peak, mittelschmerz:

• Mild pain in the ovary area is normal
• This affects only 20% of women
• Can be treated with heat or mild pain relief

Luteal phase, PMS:

• If PMS significantly affects daily functioning, consult a healthcare professional
• Natural: magnesium, B6, sleep, exercise
• Perspective: sometimes a PMS symptom shows that your body is telling you that you need less, not more-less work, less stress, more time for yourself

One Last Thing: Different Cycles, Different Women

Your cycle may be:

• Short (21 days)-this is normal
• Long (35 days)-this is also normal
• Irregular (19 days, then 31 days, then 26 days)-this can be normal, especially early in observation or under stress

NFP works for all cycles. There will always be a temperature rise. There will always be mucus. There will always be ovulation.

For a woman with a 21-day cycle, ovulation will come earlier. For a woman with a 35-day cycle, ovulation will come later. But the biology remains the same.

For a woman with an irregular cycle (19 days, 31 days, 26 days), NFP still applies-the pattern of temperature rise and mucus changes follows each individual cycle's ovulation point.