This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Infertility, Subject name: Gynaecology & Obstetrics
What is the cause for luteal phase defect? 
Select and explain. 
A. Progesterone is inadequately secreted, B. Excess estrogen is secreted, C. Excess progesterone is secreted, D. Both estrogen and progesterone are in excess
A: Progesterone is inadequately secreted
Answer: A: Progesterone is inadequately secreted 
Explanation: Luteal phase defect- In this condition, there is inadequate growth and function of the corpus luteum. There is inadequate progesterone secretion. The lifespan of corpus luteum is shoened less than 10days.As a result, there is inadequate secretory changes in the endometrium which hinder implantation.LPD is due to defective folliculogenesis which again may be de to varied reasons. Reference- DC Dutta's textbook of gynaecology -7th edition- page no 188