Luteal Phase
The luteal phase of the menstrual cycle is characterized by high progesterone levels with low FSH and LH levels. 1
Hormonal Characteristics of the Luteal Phase
After ovulation occurs following the mid-cycle LH surge, the menstrual cycle transitions into the luteal phase, which has distinct hormonal features:
- Progesterone levels rise sharply after ovulation and reach their peak approximately 6-8 days after the LH surge (mid-luteal phase), with levels typically ranging from 10-15 times higher than follicular phase levels 2, 3, 4
- FSH and LH levels remain low throughout the luteal phase after the mid-cycle surge has resolved 1, 2
- The corpus luteum secretes progesterone, estradiol, and inhibin A in response to tonic LH pulses, reaching peak size and secretion 6-7 days after ovulation 3, 4
Specific Hormonal Values
During the luteal phase, laboratory values demonstrate:
- Progesterone levels of 12.4 ± 2.3 ng/ml (compared to 0.65 ± 0.12 ng/ml during the follicular phase) 2
- Mid-luteal progesterone ≥6 nmol/L confirms ovulation has occurred; levels below this threshold indicate anovulation 5, 6
- FSH and LH remain at baseline levels after their mid-cycle peaks have subsided 2, 7
Clinical Significance
The luteal phase typically lasts 12-15 days and can be divided into three distinct processes 2, 7:
- Early luteal phase (luteinization): Characterized by increasing progesterone with relatively high LH levels as the corpus luteum forms 7
- Mid-luteal phase (progestation): Peak progesterone levels (≥10 μg/mg Cr PDG) with sustained low gonadotropins 7
- Late luteal phase (luteolysis): Declining progesterone as the corpus luteum regresses if pregnancy does not occur 7
Common Clinical Pitfall
Do not confuse low mid-luteal progesterone (<6 nmol/L) with "luteal phase deficiency"—this actually represents anovulation, not inadequate corpus luteum function. 6 When progesterone is this low during the expected mid-luteal phase, investigation for underlying causes such as PCOS, hypothalamic amenorrhea, or hyperprolactinemia is required 5, 6