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What are the reasons for failure of contraception during the safe period?

Aug 08, 2025 Source: Cainiu Health
Dr. Yang Ziqi
Introduction
A woman's ovulation can be affected by emotions, stress, environment, and other factors, which may cause it to occur earlier or later than expected, altering the previously estimated safe period. Sexual intercourse during this time may therefore result in pregnancy. Sperm can survive for several days within a woman's body. If sexual intercourse occurs during the safe period, the sperm may survive until the ovulation period and combine with the egg, potentially leading to contraceptive failure.

　　The failure of contraception during the safe period is generally due to unexpected changes in ovulation timing, longer sperm survival time, irregular menstrual cycles, calculation errors, or the occurrence of additional ovulation. Detailed explanations are as follows:

　　1. Unexpected changes in ovulation timing: Female ovulation can be affected by emotions, stress, environment, and other factors, leading to earlier or delayed ovulation. The originally estimated safe period may thus change, and sexual intercourse during this period may lead to pregnancy.

　　2. Longer sperm survival time: Sperm can survive for several days inside a woman's body. If sexual intercourse occurs during the safe period, the sperm might survive until the ovulation period and combine with the egg, resulting in contraceptive failure.

　　3. Irregular menstrual cycle: Women with irregular menstrual cycles cannot accurately estimate their ovulation time and the range of the safe period. When relying on this method for contraception, the probability of misjudgment significantly increases, which may lead to unintended pregnancy.

　　4. Calculation errors: Commonly used safe period calculation methods are based on average cycle lengths. In reality, most women's cycles do not strictly conform to this standard. Simply applying formulas can lead to errors, resulting in inaccurate judgment of the safe period.

　　5. Additional ovulation occurrences: A few women may experience unexpected ovulation within the safe period. This unusual situation cannot be predicted by conventional methods and directly causes the contraceptive method during the safe period to fail.

　　Contraception during the safe period is not a reliable method and carries a relatively high risk of failure. If there is no immediate plan for pregnancy, it is recommended to choose more safe and effective contraceptive methods, such as condoms or oral contraceptives.

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