Luteal Phase Defect

After ovulation, the ruptured follicle becomes the corpus luteum, which secretes progesterone to prepare the uterine lining for implantation. A luteal phase defect is thought to occur when corpus luteum function is inadequate, leading to low progesterone, a poorly developed endometrium, and possibly early pregnancy loss.

Diagnosis is controversial — a single mid-luteal progesterone level is commonly used, though its threshold and reliability are debated. In ART cycles, progesterone support (vaginal suppositories, intramuscular injections, or oral micronized progesterone) is routinely given after egg retrieval or before FET to bypass any concerns about natural corpus luteum sufficiency.