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What Actually Happens During Your Menstrual Cycle

What Actually Happens During Your Menstrual Cycle

Your period is only one small part.

Throughout her life, the average woman has around 450 menstrual cycles—the monthly hormonal process that prepares the female body for a potential pregnancy. But your menstrual cycle isn’t just a few days of bleeding each month. 

Whether you’re trying to conceive or just want to learn more about the reproductive process, you should get to know the stages of your cycle. It can also give you clues into your overall health, such as whether you may be at risk for diabetes, heart disease or potential difficulties getting pregnant. 

We spoke with Colleen Cardella, MD, an OBGYN at Novant Health Randolph OBGYN in Charlotte, North Carolina, to learn about how the menstrual cycle works, why you might experience irregularities and when they could warrant a doctor’s visit—plus, why it’s a good idea to track your cycle no matter where you are in life.

What happens during those phases?
On average, an entire menstrual cycle lasts around 28 days, though the regular range is anywhere from 25 to 35 days. Each cycle comprises two stages: follicular and luteal. Simply put, the follicular phase is the time between day one of your period to right before ovulation, and the luteal phase is from ovulation to the start of your next period. 

Here’s a closer look at what’s happening during a typical 28-day cycle:

Follicular phase: Those variations in cycle length, Dr. Cardella says, more often happen during your follicular phase. The first day of your menstrual cycle begins with menstrual bleeding, which for many women lasts for around five to eight days. Women have low levels of estrogen and progesterone—hormones responsible for the development and maintenance of the female body and preparing it for pregnancy—during this part of their cycle. 

After menstruation has ended, your estrogen levels rise steadily for the duration of the follicular phase, causing the lining of your uterus to thicken and prepare itself for a possible pregnancy.

During these first eight days of the follicular phase, your pituitary gland releases follicle stimulating hormone (FSH), which controls the menstrual cycle and production of eggs. Several follicles—fluid filled sacs, each of which contains an egg—develop on the ovaries. One follicle dominates, matures and releases an egg through a process called ovulation. This kicks off the luteal phase.  

Luteal phase: You might feel at your best—physically and emotionally—in the days before ovulation due to the high hormone levels. Ovulation occurs around day 14 when estrogen peaks, causing luteinizing hormone levels to surge, thus releasing the mature egg. Over the next week, the egg travels through one of your fallopian tubes, which connect the ovaries to the uterus. The follicle that produced the egg turns into the corpus luteum, a temporary structure that produces progesterone, which supports the fertilized egg and prepares the uterus for implantation should you become pregnant.

If you’re trying to become pregnant, having sex in the few days surrounding ovulation will increase your chances since sperm—the male reproductive cell—has the best opportunity to fertilize, or join with, a female’s egg as it travels to the uterus. Sperm can live in the female reproductive tract for 3 to 5 days. An egg, meanwhile, only stays alive for 12 to 24 hours after ovulation. 

“If our goal is for pregnancy, I usually say to start having intercourse daily or every other day around days 12 through 18 of the cycle, since ovulation typically occurs around day 14 for women with an average 28-day cycle,” says Cardella.

It’s tricky to know exactly when you’re ovulating, but there are a few clues to look for. 

“Your cervical mucus, at the time of ovulation, becomes clear, more slippery and we usually characterize it as having an egg-white consistency,” says Cardella. Meanwhile, if you’re monitoring your basal body temperature—your temp when you’re completely at rest—you might notice a slight increase around ovulation. Many couples who are trying to get pregnant also use at-home ovulation kits, which measure the amount of luteinizing hormone in your urine. 

After ovulation, your body undergoes one of two processes:

If sperm has fertilized an egg, the egg may attach to the lining of the uterus and you could become pregnant. Within a week, or sometimes a few weeks after, you might notice early signs of pregnancy, such as:

  • Delayed or missed period
  • Nausea and/or vomiting
  • Frequent urination
  • Breast tenderness and growth
  • Fatigue 
  • Food cravings

If sperm has not fertilized an egg, your estrogen and progesterone levels will drop around day 24 of your cycle. While every woman’s experience is different and can even vary cycle-to-cycle, you might experience symptoms of premenstrual syndrome (PMS). A few common ones are:

  • Bloating
  • Cramping
  • Fatigue
  • Breast tenderness
  • Mood swings

Your cycle ends when the unfertilized egg and lining of your uterus break down and leave your body. Menstrual bleeding then signals the beginning of a new cycle. 

Not all cycles are created equal
There are a variety of reasons for short or long cycles, skipped periods or cycles that seem different from one month to the next. Some factors may include: 

Age: When women typically get their first periods around ages 12 to 14, there may be some variations in cycle length and frequency. “Most young women at that age are not actually ovulating or releasing an egg, so that's where we see that irregular nature of cycles,” says Cardella. “After about two years, your periods should become pretty regular and predictable.”

On the other hand, women who are approaching menopause might have lighter or heavier bleeding, experience shorter or longer menstrual cycles or even skip a few altogether, owing to the way in which their ovaries produce different amounts of estrogen and progesterone than before. Eventually, with menopause, periods stop for good.

Certain health conditions and lifestyle factors: Some women have irregular menstrual cycles, or skip periods altogether, due to conditions such as polycystic ovary syndrome (PCOS). Significant weight loss or gain, stress or changes to your diet and exercise routine could also cause inconsistencies. 

Birth control: Combination birth control pills may help regulate cycles, and lead to lighter bleeding or missed periods entirely. The pill contains small amounts of estrogen and progestin—a form of progesterone—that work with your body to prevent the ovaries from releasing an egg each month, thus suppressing ovulation, says Cardella. 

Intrauterine devices (IUDs) can also affect your menstrual cycles. IUDs, both copper and hormonal, can cause heavier bleeding in the few months after insertion. However, copper IUDs may cause heavier periods with prolonged use, whereas hormonal IUDs may cause lighter to no menstrual bleeding with continued use. They both work by preventing sperm from fertilizing an egg. “Most women with IUDs will still continue to ovulate monthly, however, so they may notice signs of ovulation or PMS as they would in a normal cycle,” says Cardella.  

The importance of tracking your cycle
Cardella highly recommends tracking your cycle, which you can do with the help of an app or simple notebook. If you have regular periods, tracking can help you know when to expect menstrual bleeding each month and when you might be ovulating—which can help you determine when to try getting pregnant, if that’s your goal.

Another plus to tracking? It’s likely you’ll never be caught without feminine hygiene products.

Women between the ages of 20 to 40 should ideally have regular, predictable cycles, says Cardella. If your cycle is typically regular, one irregular month likely isn’t cause for concern. But if you have consistently unpredictable cycles, severe pain or heavy bleeding, logging your symptoms can be especially helpful. If you have a record of your symptoms, you can discuss any concerns with your doctor. 

If you have multiple cycles that last less than 25 days or more than 35 days, and you aren’t on a medication like birth control, then it would be good to see your OBGYN, says Cardella. See your doctor, too, if: 

  • You bleed between periods
  • Your period becomes abnormally heavy
  • Your cycles become irregular after having regular cycles
  • You haven’t had a period in more than three months
  • Your periods last longer than a week
  • Menstrual pain interferes with daily activities

Knowing what happens during your cycle is a great way to stay in tune with your body, which will help you recognize when something is off. 

“Patients shouldn't be scared to come talk to their gynecologist if they have any questions or concerns about their body or their menstrual cycle,” says Cardella. “I think it's just another way for females to feel empowered and in tune with their health. And it's another great way to make sure that they're taking good care of their bodies."

Medically reviewed in July 2019.

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