Are Menstrual Cycle Lengths of 47,38, and 40 Days Concerning?
Yes, these cycle lengths are concerning and warrant evaluation, as they meet the definition of oligomenorrhea (cycles >35 days) and are associated with increased health risks including premature mortality.
Why These Cycles Are Abnormal
All three cycle lengths exceed the normal adult range of 21-35 days, classifying them as oligomenorrhea. 1 Even for adolescents, where cycles up to 45 days can be normal, cycles of 47 days would still be considered prolonged. 1, 2
- The 47-day cycle clearly exceeds even the adolescent upper limit of 45 days 2
- The 38-day and 40-day cycles both exceed the adult normal range of 21-35 days 1, 3
- If two or more cycles are >32 days within a year, this indicates the Standard Days Method of fertility awareness would not be appropriate due to higher pregnancy risk 4
Health Implications
Women with consistently long menstrual cycles (≥40 days) face significantly elevated mortality risks. The most robust evidence comes from a large prospective cohort study:
- Women with cycle lengths of 40+ days at ages 18-22 years had a 34% increased risk of premature death (HR 1.34,95% CI 1.06-1.69) 5
- Women with cycle lengths of 40+ days at ages 29-46 years had a 40% increased risk of premature death (HR 1.40,95% CI 1.17-1.68) 5
- The association was strongest for cardiovascular disease mortality 5
- Women reporting always irregular cycles at ages 29-46 years had a 39% increased risk of premature death (HR 1.39,95% CI 1.14-1.70) 5
What These Cycles Suggest
Long, irregular cycles typically indicate anovulation or hormonal dysfunction:
- Oligomenorrhea is defined specifically as cycles longer than 35 days 1
- Secondary amenorrhea is defined as absence of menses for more than 45 days or three consecutive cycles 1, which the 47-day cycle approaches
- Common underlying causes include polycystic ovary syndrome (PCOS), thyroid dysfunction, hyperprolactinemia, or hypothalamic dysfunction 1
Recommended Evaluation
These patients require hormonal assessment and investigation for underlying causes:
- Check mid-luteal progesterone (7 days after suspected ovulation) to confirm ovulation status; levels <6 nmol/L indicate anovulation 6
- Measure FSH, LH, and calculate LH:FSH ratio (ratio >2 suggests PCOS) 6
- Assess thyroid function and prolactin levels 6
- Consider evaluation for metabolic syndrome and cardiovascular risk factors given the mortality associations 5
Important Caveats
- The increased mortality risk is slightly stronger among current smokers, so smoking cessation counseling is particularly important 5
- Energy deficiency, rapid weight loss, low body fat, high training volume, and psychological stress can all contribute to menstrual irregularities 1
- Up to 69% of dancers and collegiate long-distance runners experience menstrual disorders, so athletic history is relevant 1