Menstrual phase: definition and meaning
The menstrual phase is the first phase of the menstrual cycle, when the lining of the uterus sheds and leaves the body as a period. It starts on the first day of bleeding, which is cycle day 1, and usually lasts 3 to 7 days. Estrogen and progesterone are at their lowest during it.
What happens in the menstrual phase
When no pregnancy happens, the corpus luteum stops making progesterone. Without it, the endometrial lining breaks down. Prostaglandins make the uterus contract to push it out, which causes cramps. Meanwhile, the brain is already raising FSH to start the next cycle, so the menstrual phase overlaps with the start of the follicular phase.
How it can feel
- Cramps, lower back ache, and sometimes loose stools
- Tiredness, especially on heavy days
- Headaches as estrogen bottoms out
- Relief, for many, as PMS mood symptoms fade within a day or two
- A quieter, more inward mood: a good time for rest
Looking after yourself
Heat, gentle movement and anti-inflammatory painkillers help many people with cramps. Iron-rich food helps if your flow is heavy. Read the full guide to the menstrual phase, plus menstrual phase mood and period cramps.
See a doctor if period pain stops you doing normal things, painkillers don't help, bleeding lasts more than 7 days, or you soak through protection every 1 to 2 hours.
Frequently asked questions
Is the menstrual phase the same as menstruation?
Yes. It is the phase of the cycle during which menstruation happens.
Why do I feel better once my period starts?
PMS is driven by the hormone drop before bleeding. Once the period begins, hormones are low but steady, and for many people mood lifts within a couple of days.
Can you get pregnant during the menstrual phase?
It's unlikely but possible, especially with short cycles, because sperm can survive up to 5 days and ovulation may come early.
Sources
This page is for information only and isn鈥檛 medical advice. If something worries you, please talk to a doctor.
Keep reading
Menstrual phase: what happens on your periodThe menstrual phase explained: why your period starts, how long it lasts, what hormones do, and how mood, energy, sleep and skin usually feel.
Mood during your period: relief, low days and what's normalFeeling low, flat or weepy on your period, or finally relieved? Why mood during your period varies, what helps, and when it's worth talking to a doctor.
Menstruation: definition and meaningMenstruation is the monthly shedding of the uterine lining through the vagina, known as a period. Why it happens, how long it lasts, and what's normal.Dysmenorrhea: definition and meaningDysmenorrhea is the medical term for painful periods. The difference between primary and secondary dysmenorrhea, what helps, and when to see a doctor.
Period calculator: when is my next period?Free period calculator: enter the first day of your last period and your cycle length to see your next 6 periods. Private, instant, nothing is stored.