The Day 3 Panel: Ovarian Reserve and Pituitary Function
These hormones are drawn on cycle day 2, 3, or 4 (counting the first day of your period as day 1). Timing matters because baseline levels fluctuate throughout the cycle.
FSH (Follicle-Stimulating Hormone)
What it measures: FSH is the hormone that tells your ovaries to start developing eggs. Your brain releases FSH at the beginning of each cycle to recruit follicles.
What’s normal: 3–10 mIU/mL on day 3.
What high FSH means: When ovarian reserve is diminishing, the brain has to “shout louder” (produce more FSH) to get the ovaries to respond. An FSH above 10 suggests the ovaries are working harder than expected; above 15 indicates significantly diminished reserve. However, FSH can vary cycle to cycle, so one high reading isn’t definitive.
LH (Luteinizing Hormone)
What it measures: LH triggers ovulation. On day 3, baseline LH should be low. The ratio of LH to FSH can also be informative.
What’s normal: 2–10 mIU/mL on day 3.
What an elevated LH:FSH ratio means: An LH:FSH ratio above 2:1 on day 3 can suggest PMOS, though this isn’t present in all cases. Elevated baseline LH may also indicate the brain is compensating for ovarian dysfunction.
Estradiol (E2)
What it measures: Estradiol is produced by growing ovarian follicles. On day 3, it should be low because no dominant follicle has been selected yet.
What’s normal: 25–75 pg/mL on day 3.
What high day-3 estradiol means: A level above 80 pg/mL on day 3 can artificially suppress FSH, making FSH look normal when it might otherwise be elevated. This is why estradiol and FSH should always be interpreted together.
AMH: The Big Picture Hormone
AMH (Anti-Müllerian Hormone)
What it measures: AMH is produced by small antral follicles in the ovaries. It gives the best available snapshot of remaining egg quantity (ovarian reserve).
When to test: Any day of the cycle. AMH is relatively stable throughout the month.
| AMH Level | Interpretation |
|---|---|
| Over 3.0 ng/mL | High reserve (may indicate PMOS if very high, e.g., above 5.0) |
| 1.0–3.0 ng/mL | Normal reserve for reproductive-age women |
| 0.5–1.0 ng/mL | Low-normal to diminished reserve; may affect IVF response |
| Below 0.5 ng/mL | Significantly diminished reserve; time-sensitive decisions |
Progesterone: The Ovulation Confirmation
When to test: 7 days after ovulation (not necessarily “day 21”—adjust for your actual ovulation day).
What’s normal: Above 3 ng/mL confirms ovulation occurred. Above 10 ng/mL indicates a strong corpus luteum and good luteal phase support. Some REs prefer to see 15+ ng/mL.
What low progesterone means: Either ovulation didn’t occur (very common reason for low readings on “day 21”—you may not have actually been 7DPO), or the corpus luteum isn’t producing enough to sustain the lining (luteal phase deficiency).
Thyroid: The Quiet Disruptor
TSH (Thyroid-Stimulating Hormone)
What’s normal for fertility: Most reproductive endocrinologists want TSH below 2.5 mIU/L for conception (stricter than the general population range of 0.4–4.0). Between 2.5 and 4.0 is “subclinical hypothyroidism”—you may feel fine, but it can interfere with ovulation and early pregnancy maintenance.
If TSH is elevated, your doctor will likely prescribe levothyroxine. It’s safe in pregnancy and often restores normal cycling within weeks.
Prolactin: The Unexpected Player
What’s normal: Under 25 ng/mL in non-pregnant women.
What elevated prolactin means: High prolactin can suppress ovulation and cause irregular or absent periods. Causes include stress, certain medications (SSRIs, antipsychotics), thyroid dysfunction, and rarely a small benign pituitary tumor (prolactinoma). Treatment with medication (cabergoline or bromocriptine) is usually very effective.
Putting It All Together
The power of fertility blood work is in the combination, not any single number. A normal FSH with a high estradiol might be masking diminished reserve. A low AMH with normal FSH might mean fewer eggs but otherwise healthy ovarian function. Your doctor interprets these results as a panel, alongside your age, symptoms, and other test results.
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