Figure 1 shows the relative blood concentrations of four key hormones during a typical 28-day menstrual cycle.
A patient is diagnosed with a luteal phase defect, which causes her corpus luteum to degenerate prematurely around Day 18 of the cycle instead of around Day 24.
Explain how the blood levels of progesterone, oestrogen, FSH, and LH would differ after Day 18 in this patient compared to a normal menstrual cycle, and describe the physiological consequence of these differences on the patient's fertility.
