Roughly once a month, a single egg leaves an ovary, travels into a fallopian tube, and waits about a day for fertilization. That tidy summary hides a hormonal cascade involving the brain, ovaries, and uterus working in tight synchrony. When ovulation goes smoothly, conception is mechanically possible. When it does not, missed periods, fertility problems, and irregular bleeding often follow. Understanding how the process works, and what tracking it can and cannot tell you, is a useful starting point whether you are trying to conceive or simply paying attention to your cycle.
This guide covers the biology of the menstrual cycle, the most reliable methods of tracking ovulation, common reasons it goes off track, and when irregularities warrant a workup. For broader cycle issues, see our overviews on the range of women’s health conditions and on amenorrhea.
How Ovulation Actually Works
The menstrual cycle averages 28 days but anything between 21 and 35 days is considered normal in a healthy adult, according to the ACOG patient resources. The cycle has two main phases. The follicular phase runs from day one of bleeding to ovulation; FSH from the pituitary recruits a cohort of follicles in the ovary, and estradiol from the dominant follicle thickens the uterine lining.
About 36 hours before egg release, a sharp LH surge from the pituitary triggers final maturation. The follicle ruptures, releases the egg, and converts into the corpus luteum. The luteal phase begins; progesterone rises and stabilizes the lining. If pregnancy does not occur, the corpus luteum dissolves, progesterone falls, and the lining sheds as a period. The luteal phase is consistently 12 to 14 days; cycle length variation comes almost entirely from the follicular phase.
Signs of Ovulation
Several physical signals can indicate the fertile window. Cervical mucus changes from sticky to clear, stretchy, and slippery (often compared to raw egg white) in the day or two before ovulation, driven by rising estrogen. Some women feel mittelschmerz, a brief one-sided pelvic ache lasting minutes to hours when the follicle ruptures.
Basal body temperature (BBT) rises 0.5 to 1.0 degrees Fahrenheit after ovulation, driven by progesterone. The temperature shift confirms that ovulation has happened but does not predict it. Light spotting, breast tenderness, and a slight increase in libido are also reported around ovulation, though these are inconsistent.
How to Track Ovulation
The most accurate at-home method for predicting ovulation is the urinary LH test. These tests detect the LH surge that precedes ovulation by 24 to 36 hours, giving a useful timing window for trying to conceive or planning timed intercourse or IUI. Most kits run $15 to $40 per month; reusable digital monitors cost more upfront but track the rise in estrogen as well.
Cycle tracking apps that rely only on calendar predictions are the least reliable, particularly for women with variable cycle lengths. Apps that incorporate BBT, cervical mucus observations, or wearable temperature data (such as Oura, Tempdrop, or Apple Watch wrist temperature trends) are more accurate. The fertility awareness method, when taught and practiced rigorously, can identify the fertile window with reasonable precision but takes several cycles to learn.
Ultrasound monitoring at a fertility clinic is the most precise method. Serial transvaginal ultrasounds track follicle growth, and a follow-up scan after suspected ovulation can confirm follicle collapse. Most patients only encounter this level of tracking during fertility treatment.
Common Ovulation Problems
Anovulation, the absence of ovulation, accounts for roughly 25 percent of female infertility cases per the NICHD. Several conditions disrupt ovulation:
Polycystic ovary syndrome (PCOS) is the most common cause, affecting 8 to 13 percent of reproductive-age women. Multiple small follicles develop but none becomes dominant; cycles are typically long, irregular, or absent. Diagnosis uses the Rotterdam criteria: irregular ovulation, signs of androgen excess, and polycystic ovaries on ultrasound (two of three).
Hypothalamic amenorrhea shuts down ovulation when the brain stops sending FSH and LH signals. Common triggers include low body fat, intense exercise, undereating, and severe stress. Cycles return when the underlying driver is addressed.
Hyperprolactinemia from a benign pituitary adenoma, certain medications, or hypothyroidism suppresses ovulation. A blood prolactin level identifies it, and treatment often restores cycles.
Diminished ovarian reserve and primary ovarian insufficiency reduce the available follicle pool. The AMH blood test, antral follicle count, and FSH and estradiol on cycle day 3 help characterize ovarian reserve. Premature ovarian insufficiency before 40 occurs in about 1 percent of women.
Thyroid disease in either direction (hypo or hyper) disrupts ovulation. A simple TSH test is part of any fertility workup.
When to See a Doctor
Cycles shorter than 21 days or longer than 35 days, fewer than nine periods per year, periods that suddenly stop for more than three months, very heavy or very light bleeding, severe pelvic pain around ovulation, or difficulty conceiving after twelve months of trying (six months if over 35) are reasons to seek evaluation. The Office on Women’s Health notes that occasional irregular cycles are normal during adolescence, perimenopause, and after pregnancy or birth control changes, but persistent irregularity is worth investigating.
An initial workup typically includes a careful history, a pelvic exam, a TSH and prolactin level, FSH and estradiol on cycle day 3, AMH, and sometimes a transvaginal ultrasound. Treatment depends entirely on the underlying cause; ovulation can usually be restored or supported.
Inducing Ovulation
When ovulation is the bottleneck for conception, oral medications are usually first line. Letrozole (Femara) is the preferred first-line agent for PCOS-related anovulation per the ASRM practice committee. Clomiphene citrate is an older alternative. Both are taken for five days early in the cycle and stimulate the brain to send more FSH.
If oral medications fail, injectable gonadotropins (FSH directly) are next; these require ultrasound monitoring because of the risk of multiple pregnancy and ovarian hyperstimulation syndrome. For women whose anovulation stems from low body weight or excessive exercise, restoring nutritional and hormonal balance is more durable than medication.
Frequently Asked Questions
When in my cycle am I most likely to get pregnant?
The fertile window covers the five days before ovulation and the day of ovulation itself. Sperm can survive in the reproductive tract for up to five days, while the egg is only viable for about 24 hours after release. Intercourse every one to two days during the fertile window maximizes the chance of conception.
Can I ovulate without having a period?
Yes, briefly. Ovulation can return after pregnancy or stopping birth control before the first period. This is why women can become pregnant before their cycles fully resume. Persistent absence of periods (more than three months) usually means ovulation has stopped.
Are ovulation predictor kits accurate?
Urinary LH tests reliably detect the LH surge in women with regular cycles. They can be misleading in PCOS, where chronically elevated LH may produce false positives. They also confirm a surge but not actual ovulation; very rarely, the surge happens without follicle release.
Why are my cycles suddenly irregular?
Common causes include significant weight change, new exercise routines, high stress, thyroid imbalance, perimenopause (typically starting in the early to mid-40s), recent hormonal contraception changes, breastfeeding, and PCOS. Sudden changes lasting more than three cycles deserve evaluation.
The Bottom Line
Ovulation is a tightly orchestrated monthly event whose disruption is a common, treatable cause of cycle problems and infertility. Tracking with LH tests, BBT, or cervical mucus gives reasonably reliable information about your fertile window. When cycles are persistently outside the 21- to 35-day range or you are trying to conceive without success, a basic blood and ultrasound workup can identify the underlying cause and point to specific treatment.