Natural cycle transfer of frozen embryos requires the application of progesterone to maintain pregnancy after transfer. Natural cycle transfer is indicated for patients with normal ovulation. Follicular monitoring is performed on days 10-12 of menstruation to induce follicular enlargement, and after the follicles have ruptured naturally and the endometrium has been prepared with progesterone, the thawed embryos are transferred into the uterine cavity. For patients with abnormal ovulation, frozen embryo transfer cannot be performed in a natural cycle. For women with low levels of estrogen and progesterone, progesterone supplementation is required after the transfer to maintain the pregnancy. The exact timing of the frozen embryo transfer depends on the type of embryo. The best time to transfer cleavage stage embryos is the third day after ovulation. The best time to transfer blastocysts is about five days after ovulation. Women who require assisted reproduction are advised to visit a specialized reproductive medicine center.