When should hormone levels be checked during a menstrual cycle?

When to Check Hormone Levels During a Menstrual Cycle

Hormone levels should be checked during specific days of the menstrual cycle depending on which hormones are being measured, with FSH and LH typically measured on days 3-6 of the cycle (early follicular phase), while progesterone should be measured during the mid-luteal phase (approximately 7 days before expected menses).

Timing of Specific Hormone Measurements

Early Follicular Phase (Days 3-6)

• FSH and LH: Should be measured between days 3-6 of the menstrual cycle 1

  • This timing provides the most accurate assessment of baseline gonadotropin levels
  • Measurements should be based on an average of three estimations taken 20 minutes apart
  • Abnormal findings include LH/FSH ratio >2, FSH >35 IU/l, or LH >11 IU/l

• Testosterone: Should be measured on days 3-6 of the cycle 1

  • Values >2.5 nmol/l may indicate PCOS or other androgen excess disorders

Mid-Luteal Phase

• Progesterone: Should be measured during the mid-luteal phase of the menstrual cycle 1
  • This corresponds to approximately 7 days before expected menses
  • Values <6 nmol/l indicate anovulation
  • Common causes of low progesterone include PCOS, hyperprolactinemia, and hypothalamic amenorrhea

Other Hormone Considerations

• Prolactin: Should be measured as morning resting serum levels (not post-seizure) 1

  • Values >20 μg/l are considered abnormal
  • May be mildly elevated in patients with epilepsy

• Estradiol: Should be measured during the early follicular phase (days 3-6) for baseline assessment 2

  • Can also be measured at other points to assess follicular development

Special Circumstances

For Fertility Assessment

• When using clomiphene citrate for fertility treatment:
  • Treatment should begin on or about the 5th day of the cycle 3
  • Ovulation typically occurs 5-10 days after a course of clomiphene citrate
  • Appropriate tests to determine ovulation should be performed during this time

For Premature Ovarian Insufficiency (POI) Assessment

• FSH and estradiol should be measured randomly if amenorrhea is present 1
• If oligomenorrhea is present, measure during early follicular phase (days 2-5) 1
• POI diagnosis requires two elevated serum FSH levels in the menopausal range 1

For Polycystic Ovary Syndrome (PCOS) Assessment

• Pelvic ultrasound should be performed on days 3-9 of the cycle 1
• Finding >10 peripheral cysts (2-8 mm diameter) with thickened ovarian stroma suggests polycystic ovaries

Common Pitfalls to Avoid

1. Timing errors: Measuring hormones on incorrect days can lead to misinterpretation of results

   • FSH measured outside days 3-6 may not reflect true baseline levels
   • Progesterone measured outside the mid-luteal phase may falsely suggest anovulation

2. Failure to account for hormone contraceptive use:

   • Hormone measurements should be performed after ending oral contraceptive pill/sex steroid replacement therapy use, ideally after two months without oral contraceptive pills 1

3. Single hormone measurement:

   • Relying on a single hormone measurement rather than a panel of relevant hormones can lead to incomplete assessment
   • Consider measuring FSH, LH, estradiol, and progesterone for a comprehensive evaluation

4. Ignoring cycle variability:

   • Normal menstrual cycles can range from 23-38 days 1
   • Hormone timing should be adjusted accordingly for women with shorter or longer cycles

By following these timing guidelines for hormone measurements during the menstrual cycle, clinicians can obtain the most accurate assessment of a woman's reproductive endocrine function, leading to better diagnosis and management of various gynecological conditions.