What is the probability of pregnancy after unprotected sexual intercourse 5 days prior to ovulation?

From the Guidelines

The probability of pregnancy from unprotected sex 5 days before ovulation is relatively low but still possible, estimated at around 10%. Sperm can survive in the female reproductive tract for up to 5 days, which means timing intercourse 5 days before ovulation could still result in pregnancy if the sperm remain viable until the egg is released 1. However, fertility varies significantly between individuals based on factors like age, overall health, and reproductive conditions.

Key Considerations

• Sperm viability decreases over time in the female reproductive tract
• The optimal fertility window is typically 1-2 days before ovulation through the day of ovulation itself
• Emergency contraception like levonorgestrel (Plan B) can be effective if taken within 72 hours of unprotected sex, with decreasing effectiveness as time passes 1

Recommendations for Prevention

• Consider consistent use of contraceptive methods such as condoms, hormonal birth control, or IUDs for ongoing pregnancy prevention
• Cu-IUDs are highly effective as emergency contraception and can be continued as regular contraception 1
• UPA and levonorgestrel ECPs have similar effectiveness when taken within 3 days after unprotected sexual intercourse, but UPA has been shown to be more effective than the levonorgestrel formulation 3–5 days after unprotected sexual intercourse 1

From the Research

Probability of Pregnancy

• The probability of pregnancy after unprotected sex 5 days before ovulation is not directly stated in the provided studies.
• However, studies 2, 3 suggest that ulipristal acetate, a selective progesterone receptor modulator, can delay or inhibit ovulation even when taken 24 to 48 hours prior to expected ovulation.
• According to study 4, the mechanism of action of oral emergency contraception is to delay ovulation, and current evidence reveals that it is ineffective post-ovulation.
• Study 5 found that ulipristal acetate was the optimal method of oral emergency contraception, resulting in fewer unintended pregnancies and abortions compared to levonorgestrel.

Emergency Contraception Options

• Studies 2, 3, 4 discuss the use of ulipristal acetate and levonorgestrel as emergency contraception options.
• Ulipristal acetate is effective up to 5 days (120 hours) after unprotected intercourse, while levonorgestrel is only effective up to 72 hours 2, 3.
• The copper intrauterine device is also an effective method of emergency contraception, which can be left in place for up to 10 years for long-term primary contraception 4.

Factors Affecting Pregnancy Risk

• Study 4 mentions that women who weigh more than 75 kg or have a body mass index greater than 25 kg/m(2) may have a higher risk of unintended pregnancy when using oral levonorgestrel emergency contraception.
• Study 6 found that there is limited evidence on the safety of emergency contraceptive pills among women with certain medical conditions or characteristics, but no special safety concerns were identified.
• Study 5 accounted for the potential interaction of combined oral contraceptives and obesity on emergency contraception efficacy, and found that ulipristal acetate was still the optimal strategy even in the case of obesity.