Dear Alice,

Is there ever a time when you can have sex with a girl and you don't have to worry about getting her pregnant, i.e., right after her period is finished?

Yours truly,
INTERESTED

Dear INTERESTED,

The short answer to your question is possibly, but it requires a pretty solid understanding of the female menstrual cycle — and even then is unlikely to reduce of the chances of pregnancy to zero. In addition to diving into the minutiae of menstruation, it may also be helpful to take a step back and look at pregnancy and birth control methods more generally.

Pregnancy can occur any time an unfertilized egg meets up with a live sperm cell. If you have vaginal sex "right after her period is finished," it is still possible for the egg and sperm to find each other. Wondering how this is feasible? Time for a quick biology lesson: In between one menstruation (otherwise known as the period) and the next, an egg is released from the ovary (ovulation). The menstrual cycle can therefore be divided into two distinct segments, one from menstruation to ovulation and the other after ovulation until the next menstruation. The names for these two phases are the follicular phase and the luteal phase, respectively. The follicular stage lasts anywhere from 13 to 20 days and begins on the first day of menstrual bleeding. Once ovulation occurs, the egg is open for business (a.k.a. fertile) for up to 24 hours. Ovulation is followed by the luteal stage, which lasts 10 to 16 days and begins right after ovulation ends. If you do the math, it will tell you that pregnancy is significantly less likely to occur early in the follicular phase, during menstruation. For a more thorough explanation of what’s going on below the belt, check out the Go Ask Alice! Q&A Woman’s menstrual cycle.

Based on this information, there are times during a woman’s cycle when she is less likely to become pregnant, that is, when the egg is no longer viable. Unfortunately, it may not be as easy or as simple as counting the days following the last period. The majority of menstrual cycles last between 25 to 35 and typically ovulation occurs about 14 days before the next period. However, ovulation can occur at random times during the cycle and may not occur at a predictable number of days after menstruation begins for every person. Moreover, menstruation can vary from person to person, lasting anywhere from two to eight days. Another factor to be aware of: sperm can live as long as five days in a woman’s reproductive tract waiting for the release of the egg (talk about patience!).

With those variables in mind, an individual woman can determine which days she's most fertile, using the fertility awareness method. This method of charting the menstrual cycle, tracking basal body temperature, and taking note of changes in cervical mucous can be used to reduce the risk of pregnancy by not having sex on the days deemed most fertile. But, that isn't the only way to prevent pregnancy — there are other contraceptive methods that can be used to prevent an egg-and-sperm rendezvous, including (but not limited to):

  • Male or female condoms, which physically block sperm from entering the reproductive tract.
  • Hormonal birth control (such as birth control pills, the contraceptive ring, shot, patch, or intrauterine device) prevents ovulation, so the eggs stay inside the ovaries where sperm can’t reach them.
  • "Pulling-out" occurs when the penis is withdrawn from the vagina before ejaculating, again, in an effort to keep the sperm and egg away from one other.
  • Abstinence, i.e., not having vaginal intercourse, ensures the egg and sperm aren’t even in the same zip-code.

Whether or not this information relieves your concern depends on how well you understand your partner’s unique cycle and how worrisome you find the possibility of pregnancy. If you want to try to avoid pregnancy, but don’t feel comfortable crunching the numbers, just remember that you and your partner have options! To learn more about these options, consider making an appointment with a health educator or your health care provider. You can also take a look at the Contraception category in the Go Ask Alice! Sexual and Reproductive Health archives.

Alice!

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