What hormonal changes occur during the luteal phase and at the onset of menstruation?

Hormonal Changes During the Luteal Phase and Menstruation

During the luteal phase, progesterone and estrogen levels rise significantly after ovulation, with progesterone peaking approximately 6 days post-ovulation, followed by a decline of both hormones that triggers menstruation when pregnancy does not occur. 1, 2

Luteal Phase Hormonal Dynamics

Early Luteal Phase (Days 1-6 Post-Ovulation)

• After ovulation, the ruptured follicle transforms into the corpus luteum, which becomes the primary source of progesterone and estrogen secretion. 3, 4
• Progesterone levels increase progressively during the first 6 days following ovulation, reaching peak concentrations around day 6 post-ovulation. 2
• Estrogen levels (specifically estrone-3-glucuronide) rise again during the mid-luteal phase, approximately 7-10 days post-ovulation, reaching levels 2-3 times higher than early follicular phase baseline. 1
• The corpus luteum requires pulsatile LH stimulation to maintain progesterone secretion, with LH pulses occurring every 2-4 hours during the luteal phase (slower than the 1-1.5 hour intervals seen in the follicular phase). 3, 5

Mid-Luteal Phase (Days 7-10 Post-Ovulation)

• Peak luteal function occurs around day 6 post-ovulation, with maximum progesterone and estradiol concentrations preparing the endometrium for potential implantation. 2
• The combination of elevated estrogen and progesterone during this phase leads to increased fluid retention and extravasation of intravascular volume. 1, 6
• High estrogen levels improve glucose metabolism by increasing glucose availability and glycogen storage in skeletal muscle. 1
• Progesterone causes increased protein catabolism rates, potentially requiring higher protein intake during this phase. 1, 6

Late Luteal Phase and Transition to Menstruation

• If pregnancy does not occur, the corpus luteum undergoes luteolysis, causing progesterone and estrogen levels to decline sharply. 4
• This hormonal withdrawal triggers endometrial breakdown and menstrual bleeding. 4
• The decline in progesterone removes the suppressive effect on the GnRH pulse generator, allowing LH pulse frequency to increase back to follicular phase patterns (every 1-1.5 hours). 3

Physiological Effects of Luteal Phase Hormones

Metabolic Changes

• Elevated progesterone increases ventilatory drive during the luteal phase. 1
• Women demonstrate higher rates of lipid oxidation and lower rates of carbohydrate metabolism during exercise in the luteal phase compared to the follicular phase. 1
• Estrogen enhances oxidative energy metabolism and increases free fatty acid availability. 1

Endometrial Preparation

• Progesterone transforms the estrogen-primed proliferative endometrium into a secretory epithelium optimally prepared for embryo implantation during the mid-luteal phase. 3
• Both estradiol and progesterone work synergistically to create endometrial differentiation necessary for successful implantation. 3

Common Clinical Pitfalls

• Luteal phase deficiency can occur even with normal corpus luteum function if the endometrium fails to respond appropriately to normal progesterone levels. 4
• Approximately 50% of luteal phase deficiencies result from improper GnRH pulse generator function, where excessive progesterone oversuppresses the hypothalamus, leading to insufficient LH pulses. 5
• The presence of a central fluid-filled cavity in the corpus luteum (seen in 78% of women) is a normal physiological finding and does not indicate pathology. 2