Ovulation is the moment a mature egg releases from your ovary, making it available for fertilization. It typically happens once per menstrual cycle, around day 14 in a 28-day cycle, though the exact timing varies widely from person to person. The entire process is orchestrated by a chain of hormonal signals between your brain and ovaries that begins days before the egg actually releases.
The Hormonal Chain Reaction
Ovulation starts in your brain, not your ovaries. A small region called the hypothalamus releases a signaling hormone (GnRH) that tells the pituitary gland, a pea-sized structure at the base of your brain, to produce two key hormones: follicle-stimulating hormone (FSH) and luteinizing hormone (LH). These hormones travel through your bloodstream to your ovaries, where they set the ovulation process in motion.
FSH does exactly what its name suggests. It stimulates a group of fluid-filled sacs called follicles, each containing an immature egg, to start growing. As these follicles develop, they produce rising levels of estrogen, which feeds back to the brain and fine-tunes the entire system. This back-and-forth communication between your brain and ovaries runs continuously throughout your cycle.
How One Egg Gets Chosen
Each cycle, a batch of follicles begins developing in response to rising FSH levels. But only one will release an egg. The selection process works like a competition. As the follicles grow, they collectively produce enough estrogen to bring FSH levels back down. Most follicles in the group can’t survive on less FSH, so they stop growing and break down. This is called cohort attrition.
The follicle that wins, called the dominant follicle, has a critical advantage: it becomes less dependent on FSH. It shifts to relying more on LH and develops a richer blood supply and more hormone receptors, allowing it to keep growing even as FSH drops below the threshold the other follicles need. From the moment of selection, this dominant follicle enlarges rapidly and ramps up its estrogen production, preparing for the final trigger.
The LH Surge and Egg Release
The dominant follicle’s rising estrogen eventually hits a tipping point. Instead of suppressing LH (as lower estrogen levels do), this high concentration triggers a massive surge of LH from the pituitary gland. This LH surge is the direct trigger for ovulation. The onset of the surge typically precedes ovulation by about 36 hours, while the peak of the surge comes roughly 10 to 12 hours before the egg releases. This timing is why ovulation predictor kits, which detect the LH surge in urine, can give you advance notice.
The surge causes the dominant follicle’s wall to thin and weaken. Enzymes break down the tissue, and the follicle eventually ruptures, releasing the egg along with surrounding fluid. The egg is swept into the nearby fallopian tube by finger-like projections called fimbriae, and it begins its journey toward the uterus.
What Happens Right After
Once the egg escapes, the ruptured follicle doesn’t just disappear. The remaining cells transform into a new structure called the corpus luteum, a yellow-colored mass that functions as a temporary hormone-producing gland. Its primary job is churning out progesterone, which prepares the uterine lining to support a potential pregnancy by making it thicker and more blood-rich.
If sperm fertilizes the egg and implantation occurs, the corpus luteum continues producing progesterone for about 12 weeks, sustaining the pregnancy until the placenta develops enough to take over hormone production. At that point, the corpus luteum gradually shrinks and breaks down. If fertilization doesn’t happen, the corpus luteum degenerates after about 10 to 14 days. Progesterone drops, the uterine lining sheds, and your period begins.
The Fertile Window
A released egg survives for a surprisingly short time: roughly 12 to 24 hours (estimated at about 0.7 days in research studies). Sperm, on the other hand, can live inside the cervix, uterus, and fallopian tubes for 3 to 5 days. This mismatch is what creates a fertile window that extends several days before ovulation and closes shortly after. In practical terms, the highest chance of conception comes from intercourse in the two to three days leading up to ovulation, when sperm are already waiting in the fallopian tubes by the time the egg arrives.
Signs Your Body Is Ovulating
Your body gives several signals around ovulation, though not everyone notices them.
Cervical mucus changes are one of the most reliable indicators. As estrogen rises in the days before ovulation, your cervical mucus increases in volume and becomes clear, stretchy, and slippery, often compared to raw egg whites. It can stretch about an inch or more between your fingers. After ovulation, rising progesterone causes the mucus to dry up or become thick and tacky. This shift is distinct enough that some fertility awareness methods use it as the primary way to identify the fertile window.
Basal body temperature rises slightly after ovulation. Progesterone from the corpus luteum acts on the hypothalamus to raise your resting temperature by about 0.5 to 1 degree Fahrenheit. This shift stays elevated throughout the second half of your cycle. The catch is that the temperature rise confirms ovulation already happened, so it’s more useful for tracking patterns over several cycles than for predicting ovulation in real time.
Ovulation pain, sometimes called mittelschmerz, affects over 40% of women of reproductive age. It’s typically a one-sided lower abdominal ache or sharp twinge lasting minutes to hours. The LH surge increases the contractility of smooth muscle around the follicle through a prostaglandin-mediated pathway, which likely contributes to the sensation. Some women also feel it when the follicle ruptures and fluid irritates the abdominal lining.
When Ovulation Doesn’t Happen
Cycles without ovulation, called anovulatory cycles, are more common than many people realize. Polycystic ovary syndrome (PCOS) is the leading cause, responsible for about 70% of anovulation cases. In PCOS, excess androgens prevent follicles from maturing properly. They remain small instead of progressing to the dominant follicle stage, so no egg is ever released.
Other factors that disrupt ovulation include very low body weight or body fat, often from restrictive eating or excessive exercise. In these cases, the hypothalamus reduces its output of GnRH, which means the pituitary never gets the signal to produce enough FSH and LH. This is called hypothalamic amenorrhea, and it’s the brain essentially deciding the body isn’t in a state to support a pregnancy. On the other end of the spectrum, obesity can also cause anovulation by increasing androgen production, which interferes with follicle development in a similar way to PCOS.
Primary ovarian insufficiency, where the ovaries lose normal function before age 40, and thyroid disorders can also prevent regular ovulation. Because ovulation is the product of a tightly coordinated hormonal cascade, disruptions at any level (brain, pituitary, or ovary) can shut the process down.