Irregular periods are your body's way of signaling that something is off balance. Lab tests can help identify whether the cause is hormonal, thyroid-related, or something else.
What's Considered Irregular?
- Cycles shorter than 21 days or longer than 35 days
- Significant variation in cycle length (>7 days)
- Skipped periods
- Very heavy or very light bleeding
Common Causes
- PCOS: The most common cause in reproductive-age women
- Thyroid dysfunction: Both hypo and hyperthyroidism affect periods
- Hyperprolactinemia: Elevated prolactin suppresses ovulation
- Perimenopause: Hormonal fluctuations as ovarian function declines
- Hypothalamic amenorrhea: From stress, underweight, or overexercise
- Primary ovarian insufficiency: Early decline in ovarian function
The Irregular Periods Lab Panel
Baseline Hormones (Days 1-5)
- FSH and LH
- Estradiol
- Testosterone (total and free)
- DHEA-S
- Prolactin
Thyroid
- TSH, Free T3, Free T4
- Thyroid antibodies
Other Tests
- AMH (ovarian reserve)
- Progesterone (days 19-21 if cycling)
- Fasting insulin and glucose (PCOS screening)
If Periods Are Absent
- Pregnancy test
- Prolactin
- FSH (elevated suggests menopause/POI)
References
- Practice Committee of the American Society for Reproductive Medicine. (2008). Current evaluation of amenorrhea. Fertility and Sterility, 90(5 Suppl), S219-S225.
- American College of Obstetricians and Gynecologists. (2017). ACOG Practice Bulletin No. 128: Diagnosis of abnormal uterine bleeding in reproductive-aged women. Obstetrics & Gynecology, 120(1), 197-206.
