Sex during period... on pill... Safe?

Dear Alice,

My girlfriend has been on the pill for about three months now and so far she's never missed a day. We had sex once without a condom during her period. Before my ejaculation, I made sure to withdraw. What are the odds of her getting pregnant? Should I be worried?

Dear Reader,

Cheers to your partner for her faithful use of the pill! It can be hard to remember to take them every day, and of course they're much more effective when you do! If your girlfriend has been taking birth control pills at about the same time each day, then she's very unlikely to get pregnant, period. Remember, though — to ensure your girlfriend doesn't become pregnant — she will need to start taking the active pills again at the normal time (after seven days off) because sperm can hang out in the vagina for quite a while after sex.

Incidentally, withdrawal alone isn't an effective form of contraception because knowing exactly when ejaculation will occur can be difficult to determine; moreover, pre-ejaculatory fluid may contain also sperm.

Forms of birth control like the pill, the patch, and the ring alter hormone levels so that ovulation (the release of an egg from an ovary) doesn't occur. Besides preventing ovulation, hormonal birth control uses several back-up strategies. It thickens cervical mucus, making it tough for sperm to swim through. It also alters the lining of the uterus so that even if an egg were somehow released and a strong-swimming SuperSperm did manage to make it through the thickened mucus, the fertilized egg would not implant.

Even though the pill is very effective in preventing pregnancy, it isn't 100 percent effective (you can check the exact statistics for the pill in the patient information of her pill pack). Because of this, it may be a good idea to discuss with your partner about what you both would do if pregnancy became an issue.

Also, neither the pill nor withdrawal will protect you and your partner against sexually transmitted infections (STIs). To protect against STIs, use a condom in addition to any other form of contraception (such as the pill) that you may be using. If you and your girlfriend are mutually monogamous, check out Monogamous couple: Stop using condoms? in the Go Ask Alice! Sexual and Reproductive Health archive.

Last updated Jun 12, 2015
Originally published Apr 12, 1996

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