Understanding Your Menstrual Cycle Phases and Fertility

Familiarizing yourself and understanding your menstrual cycle phases becomes incredibly important when you’re trying to conceive. In this in-depth guide, we break down everything you need to know about your menstrual cycle and how you can use it to track your fertility.

What is a menstrual cycle?

A menstrual cycle refers to the changes that your ovaries and uterine lining go through every month, which are called menstrual cycle phases.

What happens during the menstrual cycle?

During your menstrual cycle, hormones send signals to the eggs in your ovaries to tell them to mature. When an egg matures, it is ready to be fertilized by sperm—leading to pregnancy. If the egg is not fertilized, the lining of the uterus, which has thickened during your menstrual cycle phases to prepare for a possible pregnancy, will shed. The shedding of your uterine lining is your period.

When do your menstrual cycle phases begin?

The four menstrual cycle phases begin with the menstrual phase (also called menstruation), which is marked by the start of your period. Most periods will last from four to eight days, but can also be shorter or longer.

You will begin menstruating when you are of childbearing age and will stop when you hit menopause. For most, this is between the ages of 12 and 51.

What are the menstrual cycle phases?

There are four menstrual cycle phases that the body goes through to prepare for a possible pregnancy. Each of the menstrual cycle phases differs in length from person-to-person.

1.   Menstrual phase

The menstrual phase (or menstruation) is the first of the menstrual cycle phases, and is when you get your period. When an egg from the previous cycle is not fertilized, estrogen and progesterone hormone levels decrease, and the lining of your uterus sheds. The length of your period is the length of your menstrual phase.

2.   Follicular phase

The follicular phase overlaps with your menstrual phase as it begins on the first day of your period. When the hypothalamus signals the pituitary gland to release follicle-stimulating hormone (FSH), it tells the ovaries to produce follicles that contain immature eggs. The healthiest of these eggs mature, and the rest are reabsorbed by the body.

As the healthiest follicle matures, it increases your estrogen levels. This causes the lining of your uterus to thicken, which allows an embryo to grow. The length of your follicular phase will vary, but tends to range from 11 to 27 days.

3.   Ovulation phase

The ovulation phase typically lasts just 24 hours, and begins when your ovary releases a mature egg due to an increase in estrogen levels during the follicular phase. The egg then travels through the fallopian tube to the uterus, where it can be fertilized by sperm. If the mature egg is not fertilized, it will dissolve or die within 12 to 24 hours, and the uterine lining will shed.

Out of the four menstrual cycle phases, the ovulation phase is the only phase when you can become pregnant. Although this phase only lasts one day, conception can occur during the five days leading up to ovulation, as well as the day of ovulation. This is because sperm can live in the body for up to five days. As conception takes place in the fallopian tube, a fertilized egg will continue to the uterus, where it implants or attaches itself.

Ovulation occurs in the middle of your menstrual cycle phases, meaning that if you have a 28-day cycle, it will occur near day 14.

4.   Luteal phase

The luteal phase is the last of the menstrual cycle phases, and occurs after the egg has left the follicle. At this point, the corpus luteum forms on the ovary to support the uterus in developing a healthy fetus by producing estrogen and progesterone.

If the egg is fertilized, the corpus luteum will continue to release progesterone for about 12 weeks. Eventually, the placenta that holds the developing fetus will be able to produce enough progesterone on its own. Since the corpus luteum is no longer needed to produce progesterone, it will begin to break down.

If the egg is not fertilized, the corpus luteum will break down about 10 days after the egg leaves the follicle. Without fertilization, the egg will not require the corpus luteum to produce progesterone to support it, and it will not trigger changes in the uterine lining to support its development. Instead, your body will shed the lining and the menstrual phase will begin.

Will having sex affect your menstrual cycle phases?

Having sex will not cause your menstrual cycle phases to change unless you become pregnant. It is safe to have sex during any of your menstrual cycle phases, including when you’re on your period. You may even find that sex helps to relieve menstrual cramps and leads to shorter periods, among other benefits.

Normal vaginal secretions during your menstrual cycle phases:

As you go through the four menstrual cycle phases, you may notice changes in your vaginal secretions (also known as vaginal discharge and cervical mucus). If you previously had an IUD, took birth control pills, or another form of hormonal contraception, you may also notice a change in the consistency of your vaginal secretions when you stop.  

Vaginal secretions during and after menstruation:

Your period will usually prevent you from noticing vaginal discharge during your menstrual phase. Right after it ends, it will usually be followed by little to no discharge.

Vaginal secretions before and during ovulation:

Leading up to ovulation, your body will produce more discharge. Changes in vaginal secretions during this time can also indicate where you are in your menstrual cycle phases.

After your period and the subsequent days with little to no discharge, your body will begin to produce more secretions before ovulation. At this point, discharge may be yellow, white, or cloudy in color and have a thicker consistency. 

Right before and during ovulation, the consistency may become more watery and clear (similar to raw egg whites).

Vaginal secretions after conception:

After conception, changes in your vaginal secretions can be one of the earliest signs of pregnancy. Once the fertilized egg has attached to your uterus, secretions will likely be more thick and clear. Approximately 10 to 12 days after conception, you may also experience implantation bleeding or spotting that lasts up to 48 hours.

What is a typical menstrual cycle length?

From the start of your period to the date of your next period is your full menstrual cycle length. The average menstrual cycle length is 28 days, but it can vary widely—with anywhere from 21 to 45 days all within a normal range.

Having a regular cycle means that you can expect your period to begin after a set amount of days have passed. However, irregular cycles that cause your periods to be less predictable are common.

How do I calculate my menstrual cycle length?

You can calculate the length of your menstrual cycle phases by tracking your periods for three months.

To do this, take note of when you start your period, and then count the days in between the first day of your next period. As your menstrual cycle length may vary, tracking the distance between multiple periods will help to you determine an average. You can do this by simply marking the days on your calendar, or with the help of an app.

Can your menstrual cycle length change as you age?

Your menstrual cycle length may vary as you age. When you first begin menstruating, it’s common to have a longer and less regular cycle. As you grow older, your menstrual cycle will likely become shorter and more regular—meaning that the number of days in between your periods is more consistent.

During perimenopause (the first stage of menopause), your menstrual cycle length may become longer or shorter at different times. This will usually happen in your 40s, and begins anywhere from four to eight years before menopause. In early perimenopause, you may experience a longer menstrual cycle and get periods about a week later than you previously had. During late perimenopause, it’s normal to wait 60 days or more between periods. 

When menopause begins, your periods will stop permanently.

What other factors impact menstrual cycle length?

Different types of contraception can impact your menstrual cycle length as many of them influence your reproductive hormones. This includes intrauterine devices (IUDs) and extended cycle birth control pills. 

If you are trying to conceive and stop taking birth control pills or another form of hormonal contraception, it may take a few months for your menstrual cycle phases to return to their previous state. For example, if you had an irregular cycle before starting hormonal contraception, it will likely become irregular again once you you stop.

Other factors that can impact your menstrual cycle phases include:

•  Stress and anxiety
•  Polycystic ovary syndrome (PCOS)
• An overactive or underactive thyroid
• Uterine fibroids
• Endometriosis
• Pelvic inflammatory disease (PID)
• Premature ovarian insufficiency
• Uterine cancer and cervical cancer
• A low or high body mass index (BMI)
• High consumption of drugs and alcohol
• Breastfeeding
• Other medications, including steroids and blood thinners

When are you most fertile during your menstrual cycle phases?

You are fertile at the time of ovulation, when an egg is released from your ovary and moves to the fallopian tube where it will stay for approximately 24 hours. As sperm can live in the body for up to five days, the time around ovulation is often referred to as your “fertile window.” Typically, the days around ovulation occur 10 to 14 days into your menstrual cycle (from the first day of your period).

Researchers have also found that the probability of becoming pregnant is highest fifteen days after your last menstrual period, however differences in age and cycle regularity will impact this.

Predicting ovulation and fertility:

You can buy an ovulation predictor kit (OPK) to tell when you are at your most fertile during your menstrual cycle phases. These can be found online or over-the-counter at pharmacies and grocery stores. OPKs work by detecting an increase in the production of the luteinizing hormone through your urine. A rise in this hormone means that you are likely to ovulate within the next 24 hours. So if intercourse is timed after the surge in this hormone, you will be more likely to conceive.

An ovulation calculator can also help you pinpoint when you might be ovulating by estimating the timing of your menstrual cycle phases by tracking your periods. 

Will my body tell me when it’s ovulating?

Keeping track of your menstrual cycle phases in the best way to predict when ovulation occurs. However, the body can also show signs of ovulation that you can look out for. This includes:

• An increase in your basal body temperature, which you can keep track of by check using a digital oral thermometer before getting out of bed in the morning.
• Discharge that looks and feels similar to raw egg whites.

You may also experience:

• Cramping in the lower abdomen
• A slight twinge of pain in your side
• Light spotting
• Breast tenderness
• Bloating
• A higher sex drive