How to manage a 15-year-old female with irregular menses, normal Ultrasound (USG) pelvis findings, and a menstrual cycle lasting 4 to 5 days with a cycle length of 18 days?

Management of a 15-Year-Old with Irregular Menses (18-Day Cycle)

Initial Assessment

This adolescent has polymenorrhea (cycle length <21 days), which requires hormonal evaluation despite normal pelvic ultrasound, as cycles should range between 21-45 days in adolescents. 1

Rule Out Secondary Causes First

• Pregnancy testing with beta-hCG is mandatory if the patient is sexually active or if clinically indicated, even with reported irregular patterns 2
• Screen for sexually transmitted infections that can alter bleeding patterns 2
• Check thyroid function (TSH, free T4) and prolactin levels, as thyroid dysfunction and hyperprolactinemia commonly cause ovulatory dysfunction presenting with irregular cycles 2, 3
• Measure FSH, LH, and testosterone levels to evaluate for polycystic ovary syndrome (PCOS) or other hormonal imbalances, as PCOS is a frequent cause of menstrual disorders in adolescents 3, 4

Key Diagnostic Considerations

• While menstrual irregularity during the first 2-3 years after menarche can reflect hypothalamic-pituitary-ovarian axis immaturity, an 18-day cycle represents polymenorrhea requiring evaluation even in adolescents 4, 5
• The normal ultrasound helps exclude structural abnormalities (polyps, fibroids, anatomical anomalies) but does not rule out hormonal causes 2, 3
• Calculate the LH/FSH ratio: a ratio >2 suggests PCOS, though this is less likely if SHBG is elevated 6

Management Algorithm

If Hormonal Workup Is Normal (Functional Polymenorrhea)

For symptomatic bleeding management, use NSAIDs as first-line treatment:

• Mefenamic acid 500 mg three times daily for 5 days during bleeding episodes 6, 7
• Alternative options include naproxen 440-550 mg every 12 hours or ibuprofen 600-800 mg every 6-8 hours, taken with food 7
• Treatment should be short-term (5-7 days) during days of bleeding only 7

If NSAIDs fail after 2-3 menstrual cycles or bleeding remains unacceptable:

• Consider low-dose combined oral contraceptives (COCs) with 30-35 μg ethinyl estradiol plus levonorgestrel or norgestimate 7
• Use monophasic formulations for simplicity 7
• COCs provide cycle regulation, are completely reversible with no negative effect on long-term fertility, and are safe throughout reproductive years 7
• Extended or continuous cycles are particularly appropriate for adolescents with severe symptoms, as they minimize hormone-free intervals and optimize ovarian suppression 7

If Thyroid Dysfunction Is Identified

• Treat the thyroid disorder appropriately, as SHBG levels and menstrual patterns will normalize with thyroid hormone normalization 6
• Refer to endocrinology for specialized management of confirmed thyroid dysfunction 6

If PCOS or Complex Hormonal Abnormalities Are Found

• Refer to endocrinology and/or gynecology for specialized management 6
• PCOS should be considered as a frequent cause of menstrual disorders in adolescent girls, particularly when accompanied by evidence of androgen excess 4

Adjunctive Non-Pharmacological Measures

• Heat therapy applied to the abdomen or back may reduce cramping pain if dysmenorrhea is present 7
• Lifestyle modifications including regular physical activity and balanced nutrition may support menstrual health, though evidence for cycle regulation is limited 8

Follow-Up and Monitoring

• Monitor response to symptomatic bleeding management within 1-2 cycles 6
• Reassess if bleeding persists and remains unacceptable to the patient despite treatment, and counsel on alternative contraceptive methods 1, 6
• Evaluate patient satisfaction with hormonal treatment if COCs are initiated 6

Critical Pitfalls to Avoid

• Do not assume functional changes without excluding structural and hormonal pathology, even in adolescents 2, 3
• Do not dismiss irregular cycles as "normal adolescent variation" when cycle length is <21 days, as this represents polymenorrhea requiring evaluation 1, 9
• Do not forget to rule out pregnancy if the patient is sexually active 2
• Avoid initiating hormonal treatment without first completing the diagnostic workup, as underlying conditions like thyroid dysfunction or PCOS require specific management 6, 3
• Remember that menstrual cycle irregularity in the first years after menarche may be a symptom of pathology demanding diagnosis and treatment, not just physiologic immaturity 4