Menstruation and Sperm Viability
Menstruation will expel sperm from the body, but if you have unprotected intercourse close to ovulation, pregnancy can still occur regardless of an upcoming period.
How Menstruation Affects Sperm
Menstruation is the shedding of the uterine lining that occurs when pregnancy does not take place during a menstrual cycle. When menstruation begins:
- The endometrial lining sheds, which would expel any sperm present in the uterus
- Menstrual flow creates a mechanical pressure that helps clear the uterine cavity 1
- The flow delivers immune cells throughout the uterine cavity that can combat foreign cells including sperm 2
Timing Considerations and Pregnancy Risk
Despite menstruation's cleansing effect, timing is critical when considering pregnancy risk:
- Sperm can survive in the female reproductive tract for up to 5 days 1
- If intercourse occurs close to ovulation (days 8-19 of a typical cycle), pregnancy can still occur even if your period is expected soon 1
- The Standard Days Method identifies days 8-19 of the menstrual cycle as the fertile window when pregnancy is most likely to occur 1
Important Factors That Affect Risk
Several factors influence whether sperm will be "washed out" before fertilization can occur:
- Cycle length: Women with regular cycles of 26-32 days have more predictable fertility windows 1
- Time until menstruation: The closer you are to menstruation, the less likely pregnancy becomes
- Timing of intercourse: Intercourse within 5 days of ovulation poses the highest pregnancy risk
- Cycle irregularity: Women with irregular cycles have less predictable fertile windows, making it harder to determine risk 1
Emergency Contraception Options
If you've had unprotected intercourse and are concerned about pregnancy:
- Emergency contraception pills should be taken as soon as possible within 5 days of unprotected sex 1
- Options include:
- Ulipristal acetate (single 30mg dose)
- Levonorgestrel (single 1.5mg dose or split doses)
- Combined estrogen-progestin regimens
- A copper IUD can be inserted within 5 days of unprotected intercourse as emergency contraception 1
Key Takeaways
- Do not rely on an upcoming period to prevent pregnancy after unprotected intercourse
- Sperm can survive long enough to fertilize an egg even if your period starts a few days later
- If pregnancy prevention is desired after unprotected intercourse, consider emergency contraception rather than waiting for menstruation
- For ongoing contraception, consider more reliable methods than timing with menstruation
Remember that while menstruation does help clear the reproductive tract, it is not a reliable contraceptive method, especially if intercourse occurred during or near your fertile window.