Ovarian pain about a week before your period is most often caused by the corpus luteum, a small structure that forms on your ovary after you release an egg. This timing places you squarely in the luteal phase of your cycle, which typically lasts 12 to 14 days (though anywhere from 10 to 17 days is normal). Pain during this window is common and usually harmless, but it can also signal something worth paying attention to.
What’s Happening on Your Ovary Right Now
After ovulation, the follicle that released your egg doesn’t just disappear. It collapses, and the cells lining it transform into a temporary hormone-producing structure called the corpus luteum. New blood vessels quickly grow into it, filling its central cavity with blood. This process is designed to be self-limiting, but it can cause a noticeable ache or pressure on one side of your lower pelvis.
Sometimes the bleeding inside the corpus luteum is heavier than usual. When that happens, the structure swells into what’s known as a corpus luteum cyst. The pain comes from the cavity stretching as blood accumulates inside it. You might feel anything from a dull, diffuse tenderness to a sharper, more localized ache on one side. This type of cyst can also cause spotting or subtle changes in your period timing, which follicular cysts (the kind that form before ovulation) typically don’t.
Most functional cysts like these resolve on their own within two to three menstrual cycles without any treatment. They’re a normal byproduct of ovulation, not a disease.
Why the Pain Feels Different From Period Cramps
It helps to understand what you’re actually feeling, because ovarian pain and uterine cramping are distinct sensations that originate in different places. Uterine cramps tend to sit centrally, low in the pelvis, and often radiate into the lower back or down both legs. They have a rhythmic, squeezing quality because they’re driven by the uterus contracting.
Ovarian pain, by contrast, usually shows up on one side. It can feel like a dull ache or a lingering pressure, as though something is pushing against nearby organs like the bladder. Exercise, urination, sex, or sudden movement can make it worse. If you notice the discomfort is distinctly one-sided and doesn’t have that squeezing, wave-like pattern, it’s more likely ovarian in origin.
The Role of Prostaglandins
Your body starts ramping up production of inflammatory compounds called prostaglandins toward the end of the luteal phase. These are the same chemicals responsible for uterine contractions during your actual period, helping your uterus shed its lining. But they don’t wait neatly for day one of your period to start working. As levels rise in the days before bleeding begins, they can cause inflammation and smooth muscle contractions in the broader pelvic area, contributing to that achy, heavy feeling around your ovaries even before your period officially starts.
This is also why some people notice bloating, nausea, or bowel changes (especially loose stools or constipation) in the days leading up to menstruation. Prostaglandins affect smooth muscle throughout your pelvis, not just in the uterus.
When It Could Be Endometriosis
If the pain you feel before your period is intense, happens every cycle, or seems to be getting worse over time, endometriosis is worth considering. This condition occurs when tissue similar to the uterine lining grows outside the uterus, often on or near the ovaries. That tissue responds to the same hormonal shifts driving your cycle, so it swells, bleeds, and causes inflammation on the same schedule.
The hallmark of endometriosis pain is that it goes beyond normal cramping. It often begins days before your period and extends well after bleeding stops. You might also notice pain during sex, pain with bowel movements, fatigue, or bloating that intensifies around your period. Endometriosis is frequently underdiagnosed because people assume their pain level is normal, so persistent pre-menstrual pelvic pain that interferes with daily life is worth bringing up with a provider.
Telling Normal From Concerning
A mild, one-sided ache that comes and goes during the week before your period and resolves once bleeding starts is, in most cases, your corpus luteum doing its job. You might notice it more in some cycles than others, depending on which ovary ovulated and how much bleeding occurred inside the corpus luteum that month.
What changes the picture is the character and severity of the pain. A corpus luteum cyst can occasionally rupture, releasing blood into the pelvic cavity. Even a small amount of free fluid in the pelvis can trigger intense, sudden pain that mimics a surgical emergency. If you experience sharp, severe pain that comes on abruptly, especially with dizziness, nausea, vomiting, or feeling faint, that’s a situation that needs immediate medical evaluation. The same applies if you develop a fever alongside pelvic pain, or if the pain is so intense you can’t stand upright.
A large ovarian cyst, whether it ruptures or not, can also cause the ovary to twist on its blood supply. This produces sudden, severe, one-sided pain that typically doesn’t let up and often comes with nausea. It’s rare, but it’s a true emergency.
Patterns Worth Tracking
If this pain is new or you’re trying to figure out whether it’s something to worry about, tracking a few details across two or three cycles gives you useful information. Note which side the pain is on (it may alternate months as your ovaries take turns ovulating), when it starts relative to your period, how intense it is on a simple 1 to 10 scale, and what makes it better or worse. This kind of log makes it much easier for a provider to distinguish between normal luteal phase discomfort, a recurring functional cyst, and something like endometriosis that benefits from treatment.
Pain that stays mild, switches sides, and resolves with your period is reassuring. Pain that’s always on the same side, escalates cycle after cycle, or starts interfering with work, sleep, or sex is telling you something different.