If you’ve closely tracked your menstrual cycle, you’ve likely gained a newfound appreciation for the wonders of your body. The ebb and flow of hormones performs like a finely tuned orchestra, crescendoing at just the right time to prepare for a potential pregnancy.
But sometimes the orchestra is off-key. Here, we’ll explain the role of one leading player: progesterone.
What is progesterone?
Progesterone is an all-star female sex hormone that works on multiple fronts, but its chief job is preparing your body for pregnancy. This helpful hormone does all of this:
Thickens your uterine lining to make a welcoming environment for a fertilized egg
Concentrates mucus in your cervix to block out bacteria that might harm a pregnancy (1)
Helps maintain the uterine lining throughout pregnancy if a fertilized egg implants in the uterine wall
Helps prevent uterine contractions
Begins to prime the glands in your breasts for breastfeeding with the help of estrogen (2)
Where does progesterone come from?
Progesterone is made by your ovaries, placenta (if pregnant), and adrenal gland. When you ovulate, the corpus luteum in your ovaries produces progesterone. The corpus luteum is the structure that once housed your egg, before the follicle holding the egg ruptured, releasing the egg on its journey to hopefully meet some sperm if you are trying to get pregnant.
If you become pregnant, after implantation, your corpus luteum continues cranking out progesterone to support your pregnancy, until around 8-10 weeks, when your placenta takes over most progesterone production (3).
How does progesterone affect my period?
Your menstrual cycle — the buildup and shedding of your uterine lining — is controlled by a delicate balancing act among your hormones, including progesterone.
Before we go further, let’s begin with a short menstrual cycle 101, because understanding your cycle and how progesterone rises and falls during your cycle, is pretty fundamental.
The menstrual cycle occurs in three phases: the follicular phase, ovulation, and the luteal phase. On the first day of your cycle, which is the first day of your period, progesterone levels are low.
How low? Your body may make only a single milligram (mg) per day of progesterone in the follicular phase, per The Journal of Clinical Endocrinology and Metabolism (4). In the run-up to ovulation, daily progesterone production ticks up to 4 mg per day, then soars to 25 mg daily around the middle of the luteal phase.
The rise and fall of progesterone helps to signal to your uterine lining to shed at the right time, triggering your period. Except sometimes low progesterone causes the lining to slough off a bit or even shed too soon, causing irregular periods or spotting.
How does progesterone cause irregular periods or spotting?
If your progesterone level doesn’t rise as it should during your cycle, you may experience irregular menstrual cycles. Why? A low progesterone level not only prevents your uterine lining from thickening, but it also may trigger premature shedding of the lining, resulting in a short luteal phase (5). A short luteal phase makes it challenging to get pregnant, which we’ll talk about more in a future post.
Low progesterone also may cause spotting before your period is due, if your body doesn’t make a sufficient amount of progesterone to keep your uterine lining wholly attached to your uterus (6).
Bear in mind, spotting before your period is not definitive proof of low progesterone. Still, if it happens consistently, it’s worth talking about with your doctor.
How does progesterone affect my sex drive and mood?
Progesterone can be a sexy-time party pooper, per a pair of papers published in the journal Hormones and Behavior. Study subjects reported feeling less amorous at times when their progesterone levels were higher. Researchers also found the drop in sex drive coincided with a surge in progesterone in the luteal phase — following ovulation — meaning less interest in sex at that time in your cycle makes sense from a reproductive standpoint (7, 8).
Progesterone also interacts with the chemicals in your brain, affecting your mood and overall sense of well-being. Progesterone does this is via its metabolite, a compound known as allopregnanolone (9).
Allopregnanolone works on a receptor in your brain to give you a calm, Zen-like feeling. Scientists suggest this helps explain that sleepy, low-energy feeling you can get right before your period or during the early part of pregnancy. However, for some women, the uptick in progesterone in the luteal phase can provoke feelings of anxiety (9).