During this time, if there’s sperm that migrates to your fallopian tube and meets the egg, fertilization can occur. From there, the fertilized egg continues to travel towards the uterus where it might implant in the lush uterine lining that was being built up and begin to receive nutrients. If all that happens—boom, you’re pregnant.
But, of course, not every month results in a pregnancy. Even if no sperm comes to meet the egg in the fallopian tube, the egg still travels toward the uterus, where it will break down.
As you get further from ovulation and are less fertile, you’ll see less cervical mucus in your underwear at the end of each day, regardless of whether or not you got pregnant. Instead, your discharge will likely become stickier and cloudier.
Again, if you’re on birth control that suppresses ovulation, your hormones won’t fluctuate as dramatically throughout the month, and there won’t be an egg to fertilize.
If you’re not pregnant, your hormone levels start to drop in the week before your period, which can lead to mood issues like PMS.
The unfertilized egg will break apart and your levels of of estrogen and progesterone will drop, since they don’t need to remain elevated to support the pregnancy.
If you’re susceptible to premenstrual syndrome (PMS) or its more severe sister premenstrual dysphoric disorder (PMDD), during the week or so preceding your period you might start to feel irritable, anxious, and depressed. While the mechanisms here aren’t completely clear and seem to be multifaceted, at the very least this decrease in hormones seems to contribute to the premenstrual mood changes some people experience before their periods.
Other effects of your lowered progesterone levels: Your uterine lining becomes destabilized, and it also releases prostaglandins, hormone-like chemicals that make your uterus contract. In combination, these result in your uterine lining sloughing off and you getting your period.
“If pregnancy has not occurred, the uterine lining says, ‘Bummer,’ and sheds,” Dr. Streicher says. “That’s essentially your body saying, ‘We’re not pregnant, we’re going to try again.” With that, the cycle begins anew.
That’s the menstrual cycle in a nutshell. Keep in mind, though, that the process may be different if you have certain reproductive health conditions.
Various reproductive health conditions can cause polymenorrhea (cycles that are 21 days or fewer), oligomenorrhea (cycles that are 35 days or more), or amenorrhea (missing your period for at least three cycles). They can also create periods that are way too heavy and painful to be normal. Here are a few of the biggest culprits. (Remember that treatment for each is wide-ranging, and what works best for you might be different from what works best for others. If you have one of these conditions, seeing a specialist is your best bet for finding relief.)
This is a common cause behind abnormally heavy, painful periods, along with bleeding between periods that can make it feel like your cycle is endless, Dr. Minkin says.