Pregnancy arises from the union of sperm and egg, and women of childbearing age have only one chance to release an egg during a menstrual cycle, therefore, the ability to predict ovulation directly affects future mothers’ chances of getting pregnant. There are many methods to determine ovulation, including basal body temperature measurement, cervical mucus examination and ultrasound monitoring of follicles, all of which are inseparable from the growth of follicles and changes in hormone levels. Therefore, before introducing ovulation determination, it is necessary to understand the structure and function of female reproductive organs and the mechanism of menstrual cycle regulation. The female internal reproductive organs consist of the ovaries, fallopian tubes and uterus. The main function of the ovaries is to produce eggs and synthesize ovarian hormones; the fallopian tubes are the place where eggs and sperm are combined and fertilized; and the uterus is the organ that nurtures the fetus. A menstrual cycle is essentially a process of follicular growth and development and extinction. This process is regulated by the hypothalamic-pituitary-ovarian system. After menstruation, the hypothalamus and pituitary gland in this system send messages to regulate the growth and development of follicles on the ovaries and secrete estrogen. The follicles mature when they reach a certain level of growth and development, usually above 17 mm in diameter. At this time, the amount of estrogen secreted by the ovaries gradually increases to a certain level, and the regulatory system then gives instructions to ovulate, completing the ovulation process. After ovulation, the follicle rupture mouth closes and the corpus luteum is formed. The corpus luteum secretes estrogen and progesterone. As the ovarian hormone levels change, the endometrium undergoes corresponding cyclic changes. Before ovulation, estrogen causes the endometrium to thicken and blood vessels to form and increase. After ovulation, under the action of progesterone, the endometrium becomes edematous and secretes glycogen in preparation for the fertilization of the egg. If the egg is not fertilized or if fertilization fails, the endometrium becomes necrotic and sheds, resulting in bleeding and menstruation. The menstrual cycle begins on the first day of menstruation. The average person’s menstrual cycle is 28-30 days, but it varies from person to person, so it is normal to have your ovaries ovulate 5 days early or late. We can observe the development of follicles and hormone secretion to look for signs of ovulation and determine the time of ovulation. There are several common methods: (1) Menstrual cycle projection method: Women of childbearing age usually ovulate one egg per month, alternating between the left and right ovaries, or continuously from one ovary to the other. Ovulation usually occurs in the middle of the menstrual cycle, about 14 days before the next menstrual period. The egg can survive for about 24 hours and the sperm can survive in the woman’s body for 3-5 days. Continuous intercourse during ovulation or intercourse on the next day of ovulation can help conception. However, ovulation is affected by environment, emotions, health condition, sex life, medication and other factors, sometimes ovulation can be early or delayed. Often, the date of ovulation cannot be determined simply by projecting the menstrual cycle. Especially for women with irregular menstrual cycles, the date of the next menstrual period is not easy to predict, so they must resort to other methods. (2) Basal body temperature detection method: The basal body temperature rises after ovulation. This is because the progesterone secreted by the corpus luteum after ovulation has the effect of raising the body temperature, which can raise the body temperature by 0.2-0.4℃ and maintain it for 12-14 days. This method requires a special basal thermometer with a rounded front end (available in major pharmacies. If you can’t get one, you can use a regular thermometer instead, but you need to be careful with the safety), which has a minimum scale of 0.05°C. Take a sublingual temperature for 5 minutes in the early morning before you wake up and do any activity. The temperature before ovulation continues to be around 36.5°C and fluctuates within 0.1°C. This is the low-temperature phase, which is the follicular phase. In the morning after the end of the low temperature period, a temperature 0.3-0.4℃ lower than the previous day will appear, which is the day of ovulation. Soon after ovulation the body temperature rises by about 0.2-0.4°C and enters the high temperature phase, the luteal phase. This high temperature will last for about 12-14 days. If the basal body temperature rises for more than 14 days in a row, you should consider whether you are pregnant and go to the hospital for examination as soon as possible. If the basal body temperature is elevated for less than 12 days, you should consider whether the luteal function is insufficient and visit the hospital as well. People who work long hours at night need to be monitored after 6-8 hours of rest. Basal body temperature monitoring is simple and convenient. The disadvantage is that ovulation can only be inferred and estimated from the previous month, and the basal body temperature is greatly affected by emotions, activities and other factors, and there are errors, making it difficult to determine the ovulation period. (3) Cervical mucus examination method: Estrogen will increase the secretion of cervical mucus to facilitate sperm movement and survival. Therefore, as estrogen secretion increases before ovulation, cervical mucus appears from a trace amount at the beginning, clear and transparent, gradually increasing to the highest amount on the day of ovulation and spreading to the vagina and vulva, making them moist and lubricated. It is generally believed that the cervical mucus on the day of ovulation is clear and transparent, egg-white in shape, with a drawing length of 10 cm or more. After ovulation, the amount of cervical discharge gradually decreases and turns cloudy and thick. In the days after menstruation, women have low estrogen levels, low cervical mucus volume and dry vagina and vulva. Observation of cervical mucus needs to be done several times a day and can usually be done by using the opportunity after waking up, before bathing or before urinating. One is to wipe the vulva with clean, white toilet paper and observe the mucus on the paper. The second is to take mucus from the vaginal opening with your finger and observe the appearance and consistency of the mucus on your finger as well as the pulling reaction with your finger. Gradually train yourself to judge the secretion of cervical mucus and record your observations in detail to determine the day of ovulation. (4) Urine LH test paper method: After the follicles have grown and matured, the secretion of estrogen increases to a certain level, which induces the production of luteinizing hormone (LH for short) in the blood and induces ovulation. The blood LH peak usually appears in the early morning and the urinary LH peak is 6-8 hours later than that in blood, therefore, the urinary LH should be tested after 2 pm and before 7-8 pm. The results of the urinary LH assay are very sensitive to fluid intake and the time of the assay, but it is not necessary to restrict fluid intake and it is best to avoid drinking large amounts of water for a short time before the test. The test is usually performed on the 11th-12th day after menstruation using urine LH ovulation paper (available at major hospital pharmacies and drugstores). The test is performed by immersing the end of the test strip indicated by the arrow in urine, holding it for 30 seconds and then removing it, and following the instructions to determine the test result according to the color shown on the test strip. After a weak positive test, test every 6-8 hours. A strong positive test indicates ovulation. Ovulation usually occurs within 24-48 hours of a strong positive test, when the pregnancy rate is high if you have intercourse for 2 consecutive days. However, the urinary LH peak lasts for a short period of time, only about 24 hours, and can only be detected before ovulation. Therefore, it is best to test when ovulation is expected to be imminent. (5) Observation of ovulation pain: In between periods, some women feel pain in the lower abdomen, which is called “ovulation pain”. Ovulation pain is a painful sensation caused by the ovum being expelled from the ovary and is a sign of ovulation, usually occurring 2-3 hours before or at the time of ovulation. Some people may feel a sudden pain in the lower left or right side of the abdomen, while others may feel like a cramp or a bout of gas. Sensitive people can feel it the day before ovulation, and the pain increases at ovulation and lasts from 30 minutes to 3 hours. The pain is overwhelmingly in the left and right lower abdomen, with individuals experiencing pain near the top of the pubic bone. Ovulation pain is usually not easily noticed, but most people can feel it if they pay attention. If ovulation pain is combined with the basal body temperature method, you can get a more accurate picture of the day of ovulation. (6) Ultrasound method: At present, all major hospitals in China can use negative ultrasound to observe the development of follicles to determine the ovulation period. As mentioned before, the follicles are growing before the day of ovulation. If the observation day happens to be the day of ovulation, sometimes you can even see the follicle rupture on the ultrasound. Using negative ultrasound to detect ovulation is the most direct and accurate method, but it needs to be performed by a doctor. In addition to the above methods, there are other methods to detect ovulation, such as blood LH measurement, smear examination of vaginal exfoliated cells, progesterone level measurement, diagnostic endometrial scraping and pathological examination, etc., all of which need to be done in a hospital. These tests range from simple to complex, and you can choose one or two to apply according to your situation, and you will usually be able to determine ovulation accurately. If you have regular periods, it is recommended that you first use the menstrual cycle method to predict an approximate ovulation date, and then use any of the methods such as basal body temperature chart, urine LH test and ultrasound to determine your ovulation date. If your periods are irregular, it is recommended that you first use a basal body temperature chart or cervical mucus test and then use any of the methods such as urine LH or ultrasound to further determine your ovulation date when you are found to be close to ovulation. If you have difficulties in determining ovulation, you can consult with the obstetrics and gynecology departments and reproductive medicine centers of major hospitals. In general, the chance of a normal couple to have a natural pregnancy per menstrual cycle is about 20%. After 3-6 cycles of intercourse after accurate determination of ovulation and still no pregnancy, it is recommended that you visit a reproductive medicine center as soon as possible for further medical tests to rule out other causes of infertility.