The six commonly used sex hormone tests, namely folliculogenic hormone (FSH), luteinizing hormone (LH), estradiol (E2), progesterone (P), testosterone (T), and prolactin (PRL), basically satisfy clinicians’ screening for endocrine disorders and general understanding of physiological functions. Nowadays, many patients come to outpatient clinics and ask for sex hormone tests. Some of them just know that they need to be checked but do not know when it is appropriate to do so, while some say that the doctor ordered them to be checked on the third day of menstruation. In my personal experience, I think there are several key time points for sex hormone test, which have different meanings. First, the third day of menstruation is the time to check basic endocrine secretion. At this time, we are not looking at how low E2 is to determine whether estrogen is insufficient, as it is originally low at this stage. Rather, E2 should be less than 50 ng/L at this stage. If it is higher than this value, it indicates poor ovarian reserve, which often leads to early menstruation, once in 21-25 days. FSH above 10 IU/L at this time also indicates poor ovarian reserve. At this time, progesterone is definitely low. Some doctors only check the five items of basic endocrinology without checking progesterone for this reason. At this time, both LH and FSH should be in the range of 3-7 IU/L and the values should be close to each other. The endocrine test on the third day of menstruation (withdrawal bleeding) after progesterone is definitely not allowed. It takes 20 days after progesterone use to completely eliminate its effects. Therefore, the hormone level can be checked 20 days after stopping progesterone (or artificial cycle). The main purpose of this test is to check E2, LH and P. The main purpose is to see if there is a pre-ovulatory LH peak and to determine if ovulation is approaching/or has occurred, and to use ultrasound follicle monitoring to diagnose the condition and guide treatment (whether HCG injection is needed to promote ovulation and when is the best time to inject). The best time to check the luteal phase is one week before menstruation. If you take basal body temperature, it is usually checked when the basal body temperature rises 6-7 days. At this time, progesterone is theoretically at its highest level in the luteal phase, up to 40 nmol/L or more. If the time calculation is accurate (about 7 days after the blood draw) and the progesterone level is 15 nmol/L or less at this time, the diagnosis of luteal insufficiency can be considered. If the progesterone level is <3 nmol/L at this time, it can be determined that ovulation is not occurring. In addition, if you come here specifically to check sex hormones, it is recommended that blood be drawn around 9:00-9:30 am, and that the blood be drawn at the entrance of the laboratory after sitting for 10 minutes in a resting state, so that the error fluctuation is smaller. However, clinical clinics are often not able to be bound, so they will check as they come, and if they find abnormalities, they will review the test next time as required.