Leucorrhea is a fluid that is unique to women during their menstrual cycle and usually appears deep in the vagina to help clean and lubricate the vagina. While it's normal for vaginal discharge to change during the menstrual cycle, some people may be confused about which day of their menstrual cycle they think they should have sex. In fact, leucorrhea is not the only criterion for judging ovulation.

Therefore, although it is normal for leucorrhea to change during the menstrual cycle, it is not the only criterion for determining ovulation. In fact, a woman's ovulation period can only be accurately predicted if her menstrual cycle is 28 days or longer. In addition, a woman's menstrual cycle and physical condition will also have an impact on determining the ovulation period. Therefore, before having sex, women should communicate with their partners to ensure that both parties have enough time and physical strength to complete the process.

To sum up, although it is normal for leucorrhea to change during the menstrual cycle, it is not the only criterion for judging ovulation. Women should predict their ovulation period based on their menstrual cycle and physical condition, and ensure that they have sex at the right time.