Low progesterone is a symptom, follicle development is the key! Progesterone is produced by the corpus luteum, which is generated by the follicles after ovulation. There are two reasons for low progesterone: the follicles ovulate before they develop, such as small follicles ovulate; and the embryo does not develop normally, producing low HCG, which cannot stimulate the corpus luteum to produce progesterone. So low progesterone is only a symptom, and supplemental progesterone will not solve the problem of embryonic development. Only by promoting ovulation can we promote healthy follicle growth, good follicle growth, good egg discharge, good embryonic development and high HCG production; good follicle growth, healthy corpus luteum produced after ovulation, good response to HCG stimulation, high progesterone. Therefore, patients with poor follicular development or small follicular ovulation in natural cycles can consider ovulation promotion to try for pregnancy and improve follicular development.