From the Guidelines
The likelihood of pregnancy on day 5 of the menstrual cycle is low but not negligible, especially considering the potential for early ovulation and sperm survival. According to the U.S. selected practice recommendations for contraceptive use, 2013, adapted from the World Health Organization 1, if it has been more than 5 days since menstrual bleeding started, there is a theoretical risk of residual sperm in the genital tract, which could lead to fertilization if ovulation occurs. This implies that even on day 5, if the woman has had sexual intercourse since the start of her current menstrual cycle, there is a small chance of pregnancy, particularly if ovulation happens sooner than typical.
Key points to consider include:
- Ovulation timing can vary significantly between women and even in the same woman from month to month.
- Sperm can survive in the female reproductive tract for up to 5 days, making pregnancy possible if intercourse occurs during menstruation and ovulation follows soon after.
- For women with shorter menstrual cycles, day 5 might be closer to their fertile window, increasing the chance of pregnancy.
- The use of a consistent contraceptive method is recommended for reliable pregnancy prevention, given the difficulty in predicting exact ovulation timing and the unpredictability of menstrual cycles.
Given these considerations and the information from 1, it's clear that while the chances of pregnancy on day 5 are generally low, they are not impossible, and preventive measures should be taken if pregnancy is not desired.
From the Research
Pregnancy Chances on Day 5 of Menstruation Cycle
- The chances of a girl getting pregnant on day 5 of her menstruation cycle depend on various factors, including the length of her cycle, the timing of ovulation, and the survival of sperm and ovum 2.
- Studies have shown that conception probabilities are significantly different from zero from five days before ovulation to the day of ovulation itself 2.
- However, the probability of conception on day 5 of the menstruation cycle is relatively low, as ovulation typically occurs around 14 days before the start of the next menstrual period.
- A study found that ulipristal acetate, a selective progesterone receptor modulator, can delay or inhibit ovulation even when taken 24 to 48 hours prior to expected ovulation 3, 4.
- Another study compared the efficacy of ulipristal acetate with levonorgestrel for emergency contraception and found that ulipristal acetate provides women and health-care providers with an effective alternative for emergency contraception that can be used up to 5 days after unprotected sexual intercourse 5.
- The probability of conception on different days of the cycle with respect to ovulation has been investigated using mathematical models, which suggest that conception is most likely to occur on only six days in each cycle 2.
- A study analyzing pooled data from three randomized trials of emergency contraception regimens found that ulipristal acetate prevents ovulation more effectively than levonorgestrel, with a delay of at least 5 days in 58.8% of the ulipristal acetate-treated cycles 6.