Hormone testing provides a snapshot of reproductive health, with the results offering insights into ovarian function. The menstrual cycle is a finely tuned feedback loop involving the follicular, ovulatory, and luteal phases, where hormone levels fluctuate dramatically. Timing the blood draw to specific cycle phases is necessary to capture accurate data. Without precise timing, the hormone level measured may be misleading, making it impossible to assess the body’s reproductive status correctly.
Baseline Hormone Assessment in the Early Cycle
Assessing specific hormones in the early part of the menstrual cycle establishes a functional baseline before the ovary begins its primary work for that month. Testing is typically performed on Cycle Day 2, 3, or 4, with Day 3 often used as the standard reference point. This timing ensures the hormones are measured when they are at their most stable, prior to the selection and growth of a dominant follicle.
The primary hormones evaluated during this early follicular phase are Follicle-Stimulating Hormone (FSH), Luteinizing Hormone (LH), and Estradiol (E2). FSH stimulates the growth of small sacs called follicles in the ovaries. A high FSH level, generally above 10 mIU/mL on Day 3, suggests the body is working harder to stimulate the ovaries, which may indicate a diminished ovarian reserve.
Estradiol is also checked at this time because high levels can artificially suppress FSH, leading to a misleadingly normal FSH result. A baseline Estradiol level should be low, typically less than 50 pg/mL, confirming that the ovaries are at a resting state. An elevated early-cycle Estradiol can indicate an active follicle or cyst is already producing estrogen, which obscures the true baseline reading.
Luteinizing Hormone (LH) is also measured, though its level is expected to be low, usually under 10 IU/L, at this point in the cycle. This early-cycle assessment provides a general view of ovarian aging and the communication axis between the brain and the ovaries. Women with conditions like Polycystic Ovary Syndrome (PCOS) may exhibit a higher baseline LH level, which is another useful diagnostic marker.
Confirming Ovulation with Luteal Phase Testing
To confirm that ovulation successfully occurred, testing for Progesterone (P4) is required during the second half of the cycle, known as the luteal phase. After the egg is released, the remnant follicle transforms into the corpus luteum, which produces Progesterone. This hormone prepares the uterine lining to be receptive for a potential pregnancy.
The ideal timing for this test is when Progesterone output is at its peak, which occurs approximately seven days after ovulation. In a standard 28-day cycle, this time frame aligns with Cycle Day 21, which is why the test is often referred to as a “Day 21 Progesterone.” However, the timing is relative to ovulation, not the cycle day itself.
If a person’s cycle is longer or shorter than 28 days, or if ovulation is tracked by other means, the test should be scheduled exactly seven days past ovulation (DPO). A Progesterone level above 5 ng/mL confirms that an egg was released. A level above 10 ng/mL suggests a strong ovulation and a healthier luteal phase, which is important for supporting early pregnancy.
Mid-Cycle Tracking for Peak Ovulatory Hormones
Mid-cycle tracking focuses on predicting and pinpointing the surge of Luteinizing Hormone (LH) that triggers the release of the egg. This LH surge is a rapid increase in the hormone that precedes ovulation by about 24 to 36 hours. The surge is the most reliable marker for identifying the most fertile period in the cycle.
Due to the brief nature of the surge, daily testing is often needed to capture the peak. At-home ovulation predictor kits (OPKs) measure LH levels in the urine and are the most common way to track this event. Testing typically begins several days before the expected fertile window, based on the person’s typical cycle length.
For a person with a regular 28-day cycle who ovulates around Day 14, testing might begin on Cycle Day 10. Once the LH surge is detected, it signals that ovulation is imminent and the fertile window is open. This tracking method is focused on immediate fertility planning rather than a diagnostic assessment of hormone health.
Hormones Tested Independently of Cycle Timing
Some reproductive hormones remain relatively stable throughout the menstrual cycle, meaning their testing does not need to be timed to a specific cycle phase.
Anti-Müllerian Hormone (AMH)
AMH reflects the total number of eggs remaining in the ovaries, known as the ovarian reserve. AMH is produced by the granulosa cells of small follicles and can be measured on any day of the cycle.
Thyroid-Stimulating Hormone (TSH)
TSH is a routine part of a reproductive hormone panel because thyroid function strongly influences the menstrual cycle and fertility. Levels that are too low or too high can affect ovulation and increase the risk of miscarriage. TSH testing is not dependent on cycle timing and can be drawn at any time.
Prolactin
Prolactin is primarily associated with milk production. Elevated Prolactin levels can interfere with the signals needed for ovulation, leading to irregular or absent periods. While it can be tested any day, a fasting, early-morning blood draw is often recommended to minimize minor fluctuations caused by stress or exercise.