Pregnancy After Taking the Plan B Pill

Plan B, also called emergency contraception, prevents unwanted pregnancies after unprotected sex or if the first form of birth control, like a condom, fails. The hormone in Plan B, levonorgestrel, keeps the ovaries from releasing an egg. points out that Plan B thins the uterine lining, which prevents the egg from implanting; the drug also thickens cervical mucus, which keeps the sperm from reaching the egg. Plan B is not 100 percent effective, so a pregnancy after taking Plan B may occur.

Time Frame

Planned Parenthood explains that women can take Plan B up to 120 hours after sexual intercourse. But the sooner a woman takes Plan B, the more effective the drug is. The McKinley Health Center at the University of Illinois notes that Plan B is 95 percent effective when taken within 24 hours; the effectiveness drops to 61 percent if taken 48 to 72 hours after intercourse.

Proper Use


How Long Does Plan B Last?

Learn More notes that women should take Plan B as soon as they can. With the Plan B version that contains two pills, women take the second pill 12 hours after the first. Plan B One-Step only has one pill. Since Plan B can cause nausea, Planned Parenthood recommends using an anti-nausea medication an hour before to prevent vomiting.

Effects on Existing Pregnancy

Kristi Monson, PharmD, and Arthur Schoenstadt, MD, authors of the eMedTV article “Plan B and Pregnancy,” point out that Plan B will not terminate an already existing pregnancy. Since the hormones in Plan B affect ovulation, the cervical mucus and the uterine lining, it cannot cause an abortion. Women who know they are pregnant should not use Plan B.



Side Effects Days After Plan B

Learn More

Specific factors can increase the likelihood of becoming pregnant after taking Plan B. For example, the longer a woman waits to take Plan B after having unprotected sex, the higher her risk is of becoming pregnant. Planned Parenthood notes that vomiting after taking Plan B decreases the effectiveness of Plan B, as the body does not fully absorb the medication.

Warning Signs

Certain signs can indicate that Plan B did not work. For example, explains that a late period, which is a week or more late, may indicate a pregnancy. Some women may have other signs of a pregnancy. Vanessa Cullins, MD, MPH, MBA, of Planned Parenthood lists sore or enlarged breasts, frequent urination, nausea, fatigue and headaches as signs of a pregnancy.

Effects on Fertility

The Feminist Women's Health Center notes that Plan B does not interfere in a woman's ability to become pregnant in the future. Other forms of birth control, such as condoms or birth control pills, are for long-term use and can protect against unwanted pregnancies.