Three basic conditions need to be met to obtain a natural pregnancy: an open tube (fallopian tubes), a good seed (sperm and egg combine to form an embryo), and fertile ground (suitable uterine environment and endometrium). Infertility is diagnosed when a couple lives together, has a normal sex life and has been trying to conceive for more than 1 year without obtaining a pregnancy. It is then necessary to find out the cause of infertility through targeted tests so as to treat the symptoms. The six reproductive hormone tests include estrogen E2, progesterone P, androgen T, follicle stimulating hormone FSH, luteinizing hormone LH and prolactin PRL, which can be used to assess the endocrine status of female reproduction which is closely related to follicle development and egg quality. The normal female menstrual cycle includes follicular, luteal and menstrual phases, and testing for different hormones at different points in time has different implications. Young (under 35 years old) women of reproductive age who normally have regular menstruation (28±7 days) usually have normal ovulation, then it is sufficient to arrange intercourse during ovulation to try for pregnancy without hormone testing. Ovulation is usually about 14 days before the next menstrual period. If you cannot find it, you can find your ovulation date by basal body temperature (BBT) or urine ovulation test. However, if you have menstrual abnormalities such as amenorrhea, irregular periods, shortened menstrual cycles, etc., especially if you are at an advanced age (>35 years old), you will need to undergo reproductive hormone testing to understand the reserve status of your ovaries and find the cause of your abnormal periods, as well as thyroid function testing. The timing of the test and the test items vary from person to person: 1. Patients with amenorrhea can be examined at any time. Abnormal thyroid function, polycystic ovary syndrome, hyperprolactinemia, and hypogonadotropic hormone may lead to menstrual disorders, amenorrhea, and infertility. 2. Check the basal endocrine level on the 2nd-4th day of menstruation, FSH>12 IU/L or FSH/LH>3 indicates the presence of ovarian reserve function, and early preparation for pregnancy is needed. 3. In patients with irregular ovulation, ovulation can be induced by drugs, combined with ultrasound and monitoring of follicle development with three hormones (E2, P, LH). Before ovulation, i.e. late follicular development, follicles of 18-22 mm in diameter and estrogen levels of 200 pg/ml or more indicate good follicular development. 4. In the mid-luteal phase after ovulation, the progesterone level should be >10ng/ml. Below this level there may be insufficient luteal function, which in turn leads to poor endometrial transformation, embryo non-fertilization or early miscarriage. To sum up, it depends on the patient’s own condition to decide whether the hormone level needs to be checked, when to check it and which one to check! Patients who need it are recommended to visit a reproductive endocrinology specialist and follow the doctor’s instructions.