A luteal phase defect (LPD) is an abnormally short luteal phase (time from LH surge to menses) of less than 13 days (Speroff- Clinical Gynecologic Endocrinology and Infertility 7th edition page 1036).
A luteal phase defect is usually due to low levels of progesterone production from the corpus luteum and is a form of ovulatory dysfunction.
The corpus luteum is the structure or cyst that is left behind in the ovary after the egg ovulates from the ovary during midcycle. Its job is to produce progesterone which is a hormone that supports the endometrium or lining of the uterus and it supports the pregnancy until the placenta takes over between 10 and 12 weeks of gestation.
Related Q&A:
Does a luteal phase defect impact getting pregnant?
Related Calculator: Luteal Phase Calculator - check the length of your luteal phase.
MyMonthlyCycles Members: If you're tracking your fertility cycle, easily review your luteal phase length with the Luteal Phase Report.