Effectiveness of Plan B If Taken After Ovulation

Plan B is a birth control option that is intended for use in emergency situations. When taken soon after intercourse, it can delay ovulation and prevent implantation of a fertilized egg in the uterus. However, if a woman has unprotected sex during or after ovulation, the level of the pill's reliability may change.

Definition

• Plan B is a type of birth control pill. However, it differs from other birth control pills in two ways. First, it is used to prevent pregnancy after unprotected sex has already occurred. Second, it involves taking only one pill, while other contraceptive pills often require a woman to take a birth control pill on every day of her cycle.

Use

• Plan B is emergency contraception. This means it's intended to prevent pregnancy when a woman has had unprotected sex and does not want to become pregnant or if a birth control method doesn't work as expected. For example, it may be used if a condom breaks or a couple has sexual intercourse without using any birth control at all. However, it is not the same thing as an abortion pill. According to PlanBOneZStep, it won't terminate a pregnancy if a woman has already become pregnant.

Timing

• You can take Plan B up to three days, or 72 hours, after having unprotected sexual intercourse. According to Planned Parenthood, it works by releasing a high level of a hormone called levonorgestrel--found in many birth control pills--into the body. This prevents your body from ovulating--releasing an egg. Since a pregnancy cannot occur unless an egg meets and is fertilized by a sperm, delaying ovulation can prevent pregnancy. Additionally, the pill makes your cervical mucus--mucus that moves from the opening of the uterus to the vagina--thicker, making it harder for sperm to travel toward an egg if you do release one. It also thins the lining of your uterus, possibly making it harder for a fertilized egg to implant there.

After Ovulation

• The effectiveness of taking Plan B after ovulation is uncertain. One of Plan B's jobs is to delay ovulation, preventing the egg from joining with a sperm. If you already ovulated and had sex before or during ovulation, an egg may have been fertilized. However, Plan B also thins the lining of the uterus. As such, a fertilized egg may not successfully implant there, and the egg may exit your body when you have your next period. If you ovulate, have sex when you suspect you are ovulating and take Plan B at the same time, you may have a higher chance of pregnancy. This is difficult to predict, however, as pinpointing the exact time of ovulation is hard, as is predicting how quickly a sperm will meet an egg.

Egg Longevity

• According to the American Pregnancy Association, an unfertilized egg only remains viable for about 24 hours after ovulation. As such, sexual intercourse even a couple of days after ovulation may be less likely to result in pregnancy. However, you may decide to take Plan B anyway to have a better chance of preventing an unplanned pregnancy.