Ovulation Detection and Timing

Biologic Indicators

The American College of Obstetricians and Gynecologists recommends that an increase in serum progesterone (≥5 ng/ml or ≥16 nmol/L) at mid-luteal phase (generally day 21 of a 28-day cycle) confirms that ovulation has occurred 1

The American College of Radiology suggests that transvaginal ultrasound is the preferred imaging method for monitoring follicular development and detecting ovulation 2, 3
A dominant follicle of 19 mm indicates imminent ovulation within 24-36 hours 4
Transvaginal ultrasound can show the disappearance of the dominant follicle or the formation of a corpus luteum after ovulation 3

The Centers for Disease Control and Prevention recommends that in a typical 28-day menstrual cycle, ovulation usually occurs between days 9 and 20 5
For shorter cycles (25 days), the fertile period is generally between days 6-11, with ovulation around days 11-12 4
The probability of ovulation is low during days 1-7 of the menstrual cycle 5

The World Health Organization notes that the dosage of anti-müllerian hormone and antral follicle count are the best available markers of ovarian reserve, but do not predict the exact time of ovulation 6

The European Society of Human Reproduction and Embryology states that reference methods for detecting ovulation with high accuracy (serial transvaginal ultrasound, serial serum LH measurements, laparoscopic follicular observation) are impractical for routine clinical use 7
The American College of Obstetricians and Gynecologists recommends that the progesterone test be performed around 7 days before expected menses (mid-luteal phase) for women with irregular cycles 1
Medications, particularly hormonal contraceptives, can suppress normal hormonal patterns and affect progesterone levels 1