Gynaecology & Obstetrics What is the optimal time during the menstrual cycle when serum progesterone should be drawn to confirm the diagnosis of luteal phase deficiency : A Day 18 B Day 21 C Day 23 D Day 25 💡 Explanation What is the optimal time during the menstrual cycle when serum progesterone should be drawn to confirm the diagnosis of luteal phase deficiency : ✓ Correct Answer: D. Day 25