What is a Period? Learn More About Your Menstrual Cycle
Opill® is all about contraception on your terms — and periods should be no different. Learn more about what is a menstrual cycle, how different methods of birth control may affect your period, and more.
What is a period?
A period — also known as menstruation — happens when the lining of the uterus is shed, accompanied by bleeding. Menstrual blood leaves the body through the vagina. It’s a totally normal experience after an individual goes through puberty and usually happens once a month.
How soon can you become pregnant after your first period?
It’s important to understand that you can become pregnant once menstruation starts. Sperm can live for up to 5 days inside the human body so if you are sexually active, you can become pregnant if you have intercourse in the days leading up to ovulation. Using a form of birth control is recommended – such as barrier methods, hormonal methods like Opill®, and others – if you’re sexually active and looking to prevent pregnancy.
What are the phases of a menstrual cycle?
Your menstrual cycle helps prepare your body for pregnancy each month. It’s a natural biological process experienced after puberty by people with female reproductive systems. Hormones in your body, specifically estrogen and progesterone, work together to control the menstrual cycle. That said, every person’s period is unique, with different symptoms, lengths, and patterns.
Now, let’s take a closer look at the phases of a typical 28-day menstrual cycle:
Menstrual phase
This phase begins on Day 1 of your period. The menstrual cycle is how your body prepares for a possible pregnancy each month. If pregnancy hasn’t happened, the thickened lining of the uterus—also known as the endometrium—is shed through the vagina accompanied by bleeding. Menstruation usually happens once a month (on average every 28 days). Periods can last anywhere from 2 to 7 days, but most are about 5 days.
Follicular phase
This phase starts on the first day you get your period and lasts until ovulation. The follicular phase overlaps with the menses phase and ends when you ovulate. The pituitary gland releases follicle-stimulating hormone (FSH), which stimulates the ovaries to produce several follicles.
Each follicle contains an egg. During days 10 to 14, one of the developing follicles will form an ovum, or fully mature egg. While its length can vary, the follicular phase usually lasts about 14 days.
Ovulation phase
Triggered by a surge in luteinizing hormone (LH), this phase happens mid-cycle. The ovary releases an egg which then enters the fallopian tube, where it can be fertilized by sperm. While the exact timing is different for everyone, ovulation usually occurs around day 14 in a 28-day cycle.
Luteal phase
This phase happens from about day 15 to day 28. After ovulation, your egg leaves the ovary and travels through your fallopian tubes to your uterus. The level of the hormone progesterone rises to prevent the endometrial lining from being shed and help prepare the uterus for pregnancy. If the egg is fertilized by sperm and implants in your uterine wall, you become pregnant.
If the egg isn’t fertilized, the corpus luteum degenerates, leading to a decrease in levels of estrogen and progesterone. This eventually triggers the start of menstruation when the thick lining of your uterus sheds again. The luteal phase typically lasts about 14 days.
What are the 4 stages of the menstrual cycle?
| Phase | When (approximate) | What |
| Menstrual Phase | Days 1-6 | Body sheds uterine lining and you bleed if pregnancy hasn’t occurred. |
| Follicular Phase | Days 7-14 | Ovaries begin to produce follicles, AKA immature eggs |
| Ovulation Phase | Day 14 | Ovary releases one mature egg which enters the fallopian tube. |
| Luteal Phase | Days 15-28 | Progesterone levels rise to prepare the lining of your uterus for pregnancy. If the egg is fertilized, you become pregnant. If not, uterine lining degenerates and menstruation starts. |
The exact timing of each phase can vary. All 4 phases play a crucial role in the reproductive process and the entire cycle usually lasts 28 days. Normally, it can range from 21 to 35 days in different individuals.
What is PMS?
Premenstrual syndrome (PMS) is the term for the physical and emotional symptoms that may occur before your period. Many people experience PMS in the days (or even weeks) leading up to their menstrual period.
The exact cause of PMS isn’t fully understood, but it’s linked to changes in the hormone levels of estrogen and progesterone during the menstrual cycle.
But it doesn’t just boil down to hormones. There are other factors that could contribute to the severity of PMS, including stress, genetic factors, or even chemical changes in the brain.
So, how can you know your period is coming? From mood swings to feeling more tired than usual, signs of PMS can be both physical and emotional.
What are signs your period is coming?
| Physical Symptoms | Emotional Symptoms |
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Symptoms of PMS can change month to month. Are you experiencing severe PMS that is getting in the way of your daily life? You’re not alone. Just head to a doctor to get checked out. Your local healthcare provider can offer some tips on managing PMS before your period.
Wait, what are period symptoms?
Period symptoms happen during menstruation. Some people experience pain with their periods, ranging from dull achy cramps to more intense pain that is difficult to manage. Talk to your doctor if you are experiencing severe pain during menstruation.
Some other period symptoms include:
Menstrual cramps
As your body sheds the uterine lining, uterine contractions may cause pain in the lower abdomen and/or back.
Bleeding
The primary symptom of your period involves shedding of the uterine lining. The flow can vary from light to heavy and usually lasts 2 to 7 days.
Bloating
Some people feel swelling in the abdomen.
Breast tenderness
Hormonal changes can cause breasts to feel swollen, tender, or painful.
What are the best ways to alleviate period symptoms?
Let’s be real. Period symptoms aren’t fun — but there are a few ways to help. Sit back, relax, and run yourself a hot bath. (You deserve it.)
Here are some other tips that can help ease cramps:
- Over-the-counter pain medication, like ibuprofen (Advil), naproxen (Aleve), or acetaminophen (Tylenol). Be sure to always follow instructions on the label and consult with your doctor.
- Exercise
- Rest
- A warm bath or heating pad
- Having an orgasm (by yourself or with a partner)
Irregular vs. Regular Periods: How long does a period last?
A typical period usually lasts 2-7 days and occurs roughly every 28 days.
What is considered an irregular period? Periods that occur fewer than 21 days or more than 35 days apart, missing three or more periods in a row, or a menstrual flow that becomes much heavier or lighter than usual may be considered abnormal. Talk to your doctor if you have concerns about your period.
Hormone levels, increased stress, medication changes, certain types of birth control, changes to your birth control, and certain health conditions can also cause irregular periods.
When should I worry about my period?
Remember: Cramps and bleeding are a totally normal part of getting your period. But some people get symptoms that are so painful it’s hard to do everyday activities. Is your period pain so bad you can’t easily navigate work or school? Does over-the-counter medicine not help? Then you may want to consult with your doctor.
Take a pregnancy test or talk to a doctor if your period is late after contraception failure – for example, after missing any birth control pills or condom breakage, if you have not had a period for 2 months, or if you think you may be pregnant.
You deserve education, empowerment & control — period.
Understanding your menstrual cycle is key to knowing your body and making informed health decisions. At Opill®, we believe access to accurate information is important for navigating your reproductive health journey.
Take the next step in understanding your options and making choices that are right for you by exploring our other resources and frequently asked questions about Opill®.
*Opill® does not prevent ovulation in all cycles.
Sources
The menstrual cycle: Menstruation, ovulation, and how pregnancy occurs. ACOG. (2022, January). https://www.acog.org/womens-health/infographics/the-menstrual-cycle. Accessed January 2025.
All about periods (for teens). Nemours® TeensHealth. (2024, July). https://kidshealth.org/en/teens/menstruation.html. Accessed January 2025.
Your menstrual cycle. Office on Women’s Health. U.S. Department of Health & Human Services. https://womenshealth.gov/menstrual-cycle/your-menstrual-cycle. Accessed March 2025.
Menstruation and Menstrual Problems. National Institute of Child Health and Human Development. https://www.nichd.nih.gov/health/topics/factsheets/menstruation. Accessed March 2025.
