What is the cause for luteal phase defect?

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