Hypothalamic Amenorrhea in a Runner Who Wants to Conceive

Mechanism

• This is functional hypothalamic amenorrhea: chronic energy deficiency (high exercise load, inadequate carbohydrate intake, low BMI) suppresses hypothalamic GnRH pulse frequency. Low LH pulsatility gives low estradiol (24 pg/mL), and the negative progesterone challenge confirms an estrogen-deficient, non-ovulatory endometrium.
• This is an adaptive response to perceived energy scarcity, not a primary ovarian or pituitary lesion. The normal FSH and normal prolactin/TSH make pituitary disease and hyperprolactinemia unlikely, but a low FSH with low estradiol in a woman with headache or visual symptoms would still warrant pituitary imaging.

Why the combined oral contraceptive is the wrong tool for fertility

• It does not restore hypothalamic signaling; it replaces it with a pharmacologic cycle and, once stopped, the underlying energy deficit is unchanged.
• It masks the return of menses as an outcome measure and can be mistaken for recovery.
• It raises sex hormone-binding globulin and generally does not restore ovulation.
• If she took it for a year and then stopped, she would likely have no more fertility than today, having lost a year of bone-protective and behavioral work.

What actually works for her fertility

• Restoration of energy balance: reduce training, increase caloric and carbohydrate intake, gain 2–3 kg. Cognitive behavioral therapy has randomized evidence in this population and may be more acceptable to her than "eat more."
• If menses do not return despite this, refer to reproductive endocrinology for pulsatile GnRH or gonadotropin therapy. Clomiphene alone typically fails because there is no estrogen priming to antagonize.

Why not a bisphosphonate

• A Z-score ≤ −2.0 in a premenopausal woman is "below the expected range for age," but bisphosphonates are not approved for premenopausal osteoporosis, are not indicated without fragility fracture in most cases, and are contraindicated in pregnancy. They deposit in bone with a skeletal half-life measured in years, and she hopes to conceive within 12 months. The same objection applies to denosumab, which also risks rebound vertebral fractures on cessation.
• Giving a bisphosphonate here would be the classic error: treating a number rather than a mechanism.

What to do

1. Transdermal estradiol 100 mcg/day with cyclic micronized progesterone 200 mg - physiologic replacement that protects bone without suppressing the axis in the way a combined oral pill does. Transdermal is preferred because oral estrogen undergoes hepatic first-pass metabolism and suppresses IGF-1, blunting bone formation. Stop when pregnancy is achieved.
2. Correct vitamin D (24 ng/mL) to >30 ng/mL with supplementation, and ensure calcium intake of ~1,000–1,200 mg/day from diet.
3. Weight-bearing and resistance exercise - she already runs, but 60–70 km per week may itself be part of the problem; a balanced program plus reduced mileage.
4. Repeat DXA no sooner than one to two years; the changes are slow and frequent scans generate anxiety without changing management.
5. Address the root cause with the behavioral and nutrition plan above - menses returning is the best biomarker that bone protection is working.

• Screen for other secondary causes once: celiac serology if GI symptoms or iron deficiency, and consider repeat TSH and estradiol at follow-up.

Pregnancy risks in this context

• Low BMI before conception increases risks of fetal growth restriction, preterm birth, and low birth weight; undernutrition before and during pregnancy matters more than the hormone manipulation that achieved conception.
• Gonadotropin ovulation induction carries a higher multiple-gestation rate than spontaneous conception; she should have an early dating ultrasound.
• Untreated estrogen deficiency and low bone density mean pregnancy and lactation will be a substantial skeletal stress; she should not enter lactation with an uncorrected deficit if it can be avoided.

Follow-up plan

• High-risk obstetric co-management with early nutrition and dietitian input, aiming for appropriate gestational weight gain rather than continued restriction.
• Stop transdermal estradiol and progesterone once pregnancy is confirmed.
• Screen for gestational diabetes if clinically indicated and monitor for anemia.
• Discuss breastfeeding duration and ensure adequate calcium and vitamin D during lactation.
• After delivery and weaning, reassess: if she returns to 60–70 km per week and the same intake, amenorrhea will recur and bone loss will resume. Restart bone-protective estradiol if she is not menstruating and not trying to conceive.
• Repeat DXA one to two years postpartum, and document a clear contingency plan with her about training volume - the honest message is that exercise reduction is a treatment, not a lifestyle preference.