Reasons why ovulation cannot be detected during ovulation period:

1. Insufficient number of eggs: Women usually have only one egg per month. If a woman has experienced multiple sexual intercourses in a short period of time, the number of eggs may be insufficient, thus affecting the test results.

2. Insufficient sperm count: If a man fails to deposit sperm in a woman’s reproductive tract, it may result in the woman not being able to detect an egg during ovulation.

3. Improper detection methods: Some detection methods may not accurately detect eggs, such as using a test tool too early or too late, or using the wrong test method.

4. Other medical conditions: Some medical conditions, such as anemia or thyroid problems, may prevent a woman from detecting eggs during ovulation.

5. Individual Differences: Everyone’s body is unique, so some women may not be able to detect eggs during ovulation, while others may not.

Although not detecting eggs does not mean that a woman cannot become pregnant, in some cases it may have an impact on a woman's reproductive health. Therefore, if a woman finds that she cannot detect eggs during ovulation, she should consult a doctor promptly to determine the cause and obtain appropriate treatment.