What are the reasons for questioning the effectiveness of fertility awareness-based (calendar) methods of contraception?

Generally, the reliability of the rhythm method (fertility awareness-based contraception) is often questioned due to factors such as susceptibility of ovulation to external influences, irregular menstrual cycles making timing difficult to predict, extended sperm survival increasing risk, calculation inaccuracies, and individual variations that undermine the stability of so-called "safe periods." A detailed analysis is as follows:

1. Ovulation is easily influenced: Women's ovulation timing can be disrupted by emotions, stress, environment, and other factors, potentially causing it to occur earlier or later than expected. This makes the calculated "safe period" inaccurate and increases the likelihood of unintended pregnancy.

2. Irregular cycles make prediction difficult: Women with irregular menstrual cycles cannot accurately predict ovulation or safe periods. Relying on this method significantly increases the risk of contraceptive failure due to miscalculation.

3. Extended sperm survival increases risk: Sperm can survive for several days inside the female reproductive tract. If intercourse occurs during the presumed safe period, sperm may remain viable until ovulation begins, allowing fertilization to occur and reducing the effectiveness of this method.

4. Calculation methods are prone to error: Commonly used calculation methods assume an average cycle length, but most women do not have perfectly regular cycles. Simply applying standard formulas can lead to inaccuracies in determining the safe period.

5. Individual differences reduce reliability: Due to physiological differences among women, even those with regular cycles may experience unexpected ovulation (such as multiple or unscheduled ovulations), making the "safe period" less reliable and increasing the chance of contraceptive failure.

When choosing a contraceptive method, it is important to recognize that the rhythm method is relatively unreliable. For individuals who do not currently wish to become pregnant, more effective methods such as condoms or oral contraceptives are recommended to reduce the risk of unintended pregnancy. Those with questions about contraception should consult qualified healthcare professionals for personalized guidance.