Free from pregnancy worries

Originally Published: November 7, 1997 - Last Updated / Reviewed On: November 9, 2004
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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,

Pregnancy can occur any time an unfertilized egg meets up with a live sperm cell. Trying to prevent this from happening is how most contraceptive methods work. For example:

  • Condoms physically block sperm from entering a woman’s reproductive tract.
  • Hormonal birth control (such as birth control pills or the contraceptive patch) prevents a woman from ovulating, so the eggs stay inside the ovaries where sperm can’t get to them.
  • "Pulling-out" or "withdrawal" is when a man withdraws his penis from the woman’s vagina before ejaculating, again, in an effort to keep the sperm and egg away from one other.
  • And there’s always abstinence, i.e., not having vaginal intercourse, which makes sure egg and sperm aren’t even in the same zip-code.

The effectiveness of these methods and others depends upon how successful they are at preventing an egg-sperm rendezvous.

So, in order to answer your question, we need to know if having sex with a woman "right after her period is finished" could result in an egg and a sperm being in the same place at the same time. The short answer is yes, pregnancy is possible during this time. To understand how likely, a little background story on the menstrual cycle is necessary.

In between one menstruation 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 duration of these phases is described in the following table:

Phase Name Duration Comments
Follicular Phase Approximately 13 to 20 days The follicular phase starts on the first day of menstrual bleeding and ends when ovulation occurs. The length of the follicular phase is unpredictable, both from woman to woman and also from month to month for the same woman.
Ovulation   An egg is viable for fertilization for up to 24 hours.
Luteal Phase Approximately 10 to 16 days The luteal phase starts immediately after ovulation and ends when the follicular phase begins (on the first day of menstrual bleeding). The luteal phase is pretty consistent from month to month, with the average duration being 14 days.

Based on this information, there are times during a woman’s cycle when she can’t get pregnant, that is, when the egg is no longer viable. Determining when this has happened, however, isn’t as simple or easy as counting days from her last period. The majority of women have 25 - 35 day cycles and typically ovulate about 14 days before their next period. However, the remaining women may ovulate at random times during the cycle. Ovulation does not occur a predictable number of days after menstruation begins, and menstruation lasts a variable number of days (anywhere from 2 to 8). Moreover, sperm can live as long as five days in a woman’s reproductive tract waiting for the release of the egg.

However, the numbers also tell us that pregnancy is significantly less likely to occur early in the follicular phase, during menstruation. Because the follicular phase has a normal range of 13 to 20 days, the days immediately following the first day of bleeding are statistically quite unlikely to be fertile times.

Whether or not this information relieves your worry depends on how comfortable you are interpreting the numbers and how worrisome you find the possibility of pregnancy.

Alice