Low progesterone and normal HCG may be the manifestation of lesions caused by luteal insufficiency, adrenal gland function abnormality, other endocrine diseases and so on. 1. Luteal insufficiency: If the ovarian luteal insufficiency, the secretion function is obviously decreased, which may lead to the decline of progesterone in the body and cause low progesterone, while HCG is normal. 2. Adrenal gland function abnormality: when female patients have adrenal gland function abnormality, it may have certain influence on the progesterone level, which may lead to the decrease of progesterone and normal HCG. 3. Other endocrine diseases: If the female patient has abnormal thyroid function, hypothalamus or pituitary disease, it may also cause ovarian dysfunction, which may result in decreased progesterone and normal HCG. Low progesterone, HCG normal, need to go to a professional regular medical institutions for diagnosis and treatment.