During ovulation, a mature egg bursts from its follicle on the surface of the ovary and enters the fallopian tube, where it can be fertilized for up to 24 hours. This event is the pivotal moment of the menstrual cycle, driven by a precise cascade of hormonal signals that build over days and culminate in a release lasting only minutes. Understanding what happens before, during, and after that release helps you recognize your body’s signals and make sense of your fertile window.
The Hormonal Buildup That Triggers Egg Release
Ovulation doesn’t happen spontaneously. It’s the endpoint of a hormonal chain reaction that starts in the brain. Early in your cycle, the pituitary gland releases follicle-stimulating hormone, which prompts several follicles in the ovaries to begin maturing. Over roughly two weeks, one follicle outgrows the rest and becomes dominant, producing rising levels of estrogen as it swells.
That climbing estrogen eventually hits a threshold that flips a switch in the brain, triggering a massive surge of luteinizing hormone (LH). This LH surge begins about 36 hours before ovulation and lasts roughly 24 hours. Ovulation itself occurs between 8 and 20 hours after the LH peak. This is the window that ovulation predictor kits are designed to detect: they measure LH in your urine to flag the surge before the egg is actually released.
What Happens Inside the Ovary
The LH surge sets off a series of structural changes in the dominant follicle. Enzymes activate that begin breaking down the follicle wall from the inside, dissolving the layers of protein and connective tissue holding the egg in place. Think of it like a controlled demolition: the wall thins at a specific spot on the ovary’s surface until it finally ruptures, and the egg, surrounded by a cluster of supportive cells, is pushed out.
The released egg doesn’t simply fall into the fallopian tube. Finger-like projections at the end of the tube, called fimbriae, sweep across the surface of the ovary and guide the egg inward. Once inside, tiny hair-like structures lining the tube create a gentle current that moves the egg toward the uterus. This journey takes several days, but the egg itself remains viable for fertilization for less than 24 hours after release.
The Follicle’s Second Life as the Corpus Luteum
After the egg escapes, the now-empty follicle doesn’t just collapse and disappear. The cells that made up the follicle wall reorganize into a new structure called the corpus luteum, a yellowish mass that seals the break and takes on a completely different job: producing progesterone.
Progesterone is the hormone that prepares the uterine lining for a potential pregnancy. It thickens the lining, increases its blood supply, and shifts the overall hormonal environment to support implantation. If the egg is fertilized and implants successfully, the corpus luteum keeps producing progesterone for several weeks until the placenta takes over. If no pregnancy occurs, the corpus luteum breaks down after about 10 to 14 days, progesterone drops, and the uterine lining sheds as your period.
Signs Your Body Gives You
Several physical changes cluster around ovulation, and recognizing them can help you identify where you are in your cycle.
The most reliable sign is a shift in cervical mucus. As ovulation approaches, rising estrogen causes the cervix to produce mucus that is clear, wet, stretchy, and slippery, often compared to raw egg whites. This consistency exists for a reason: it creates a hospitable pathway for sperm to swim through the cervix and reach the egg. After ovulation, mucus typically becomes thicker, stickier, and less noticeable.
Basal body temperature (your temperature first thing in the morning, before getting out of bed) rises slightly after ovulation. The increase is small, typically between 0.4°F and 1°F (0.22°C to 0.56°C), and it stays elevated through the rest of the cycle. Because the rise happens after the egg is already released, temperature tracking confirms that ovulation occurred rather than predicting it in advance.
About one in five women experience ovulation pain, sometimes called mittelschmerz. It’s usually a one-sided ache or sharp twinge in the lower abdomen, on whichever side released the egg that cycle. The pain can last anywhere from a few minutes to 24 or 48 hours. It’s thought to result from the follicle stretching before rupture or from the small amount of fluid and blood released when the follicle breaks open.
The Fertile Window Around Ovulation
Your fertile window is wider than you might expect. Sperm can survive inside the reproductive tract for 3 to 5 days, while the egg lives for less than 24 hours after release. That means pregnancy can result from sex that happens anywhere from five days before ovulation to one day after. In a textbook 28-day cycle, ovulation occurs about 14 days before the start of the next period, but plenty of cycles don’t follow the textbook.
The Standard Days method considers days 8 through 19 of a 26- to 32-day cycle to be the most fertile. More precise approaches combine multiple signals. The Marquette method, for instance, pairs temperature and mucus tracking with an electronic monitor that detects hormonal changes in urine. No single indicator is perfect on its own, which is why combining methods gives a clearer picture of when ovulation is approaching and when it has passed.
When Ovulation Doesn’t Happen
Ovulation isn’t guaranteed every cycle. Anovulation, where no egg is released, is common at certain life stages and under specific conditions. It happens frequently when periods first begin during puberty and again during perimenopause, when hormone levels are naturally unstable. Between those bookends, several factors can disrupt the process.
Polycystic ovary syndrome (PCOS) is one of the most common causes. Elevated androgen levels interfere with follicle maturation, so the dominant follicle never fully develops or ruptures. Obesity can contribute through a similar mechanism, as excess body fat can increase androgen production. On the opposite end, a very low body weight or intense long-term exercise can suppress the pituitary signals (LH and FSH) needed to drive the whole process forward.
Thyroid dysfunction, high prolactin levels, pituitary gland problems, and primary ovarian insufficiency can all cause anovulation as well. Excessive stress plays a role too, disrupting the hormonal relay between the brain and the ovaries. If your cycles are very irregular, unusually short, or unusually long, or if you never notice any of the physical signs described above, anovulation may be the reason.