When to Take a Pregnancy Test After Plan B

While Plan B is highly effective, it does not always work to prevent pregnancy. If your period is late, consider taking a pregnancy test.

Did you have unprotected sex? Forget to take your pill? Perhaps the condom broke? If so, you may be pregnant. If you’re not ready to have a baby, Plan B One-Step emergency contraception is an effective way to stop a pregnancy before it begins.

Often referred to as the “morning after” pill, Plan B works by stopping the release of an egg from the ovary, hence preventing pregnancy from taking its course. However, Plan B is most effective when taking as directed.

Plan B One-Step is a single tablet containing levonorgestrel, a common hormone found in many birth control pills according to Foundation Consumer Healthcare. An estimated 7 out of 8 women who would have fallen pregnant will not become pregnant after taking Plan B.

“If you take it within 72 hours after you’ve had unprotected sex, Plan B One-Step can reduce the risk of pregnancy by up to 89%,” says WebMD. “If you take Plan B One-Step within 24 hours, it is about 95% effective.”

While Plan B is highly effective, it does not stop pregnancy from occurring 100% of the time. If you miss your next period, take a pregnancy test to determine if you’re pregnant.

What the Experts Say

If taken within a few days after unprotected sex, Plan B One-Step can prevent pregnancy from occurring. However, it will not stop a pregnancy that has already developed. Learn more about how Plan B works.

“In Plan B, levonorgestrel prevents pregnancy in the same manner as when it is taken as a daily oral contraceptive, that is, by preventing ovulation. If the woman is already pregnant when she takes Plan B, the drug does not cause a spontaneous abortion.”

– Diane S. Aschenbrenner, Samatha J. Venable, Drug Therapy in Nursing

“These drugs will not terminate an existing pregnancy and will not harm a fetus if present. Recall that pregnancy is defined as implantation of a fertilized egg. Because Plan B One-Step acts before fertilization and implantation, they cannot be considered abortifacients.”

– Laura Rosenthal, Jacqueline Burchum, Lehne’s Pharmacotherapeutics for Advanced Practice Providers

“Plan B, or the so-called morning-after pill, contains the progestin levonorgestrel, a synthetic hormone used in birth control pills for over 40 years. Currently, in the United States, it can be obtained over-the-counter (i.e. without prescription) by women aged seventeen or older.”

– Gary C. Schoenwolf, Steven B. Bleyl, Larsen’s Human Embryology

“It sucks, but it happens – If the condom breaks, you forget to take the pill, or you’re on an antibiotic that might affect the results of the pill, there’s a chance you could get pregnant. In this case, take a pregnancy test (and if the condom broke, you want to get tested for STIs, too).”

– Hannah Orenstein, Here’s When You Should Take a Pregnancy Test

“Consider testing when your period is more than seven days late. If you test too soon, you could get a false negative (a negative test, even though you are really pregnant). It takes a week or two after fertilization for an egg to implant in the uterus.”

– Kristi Monson, PharmD, When to Take a Pregnancy Test

When Should I Take a Pregnancy Test After Plan B?

You’ve had unprotected sex and soon after took Plan B One-Step. Now what? If you start your period, you’re good to go. If not, you may be pregnant.

“If it has been at least 10 days since you had unprotected sex and you have not gotten your period when you think you should have, you can take a home pregnancy test to find out if you are pregnant,” says Princeton University. “Before that, a negative test result won’t be accurate, and you definitely can’t tell if you’re going to get pregnant in the first few days after sex.”

Can Plan B Harm the Baby If I’m Already Pregnant?

You may be worried that if you are already pregnant and take Plan B, you will hurt the baby. The good news is that Plan B One-Step is not an abortion pill, meaning it will not affect an existing pregnancy or cause birth defects. However, many experts recommend taking a pregnancy test prior to Plan B to ensure that you are not pregnant before taking the emergency contraceptive.

When Is Plan B Less Likely to Work?

There are certain circumstances in which Plan B is less likely to work. This includes taking it outside the recommended 72 hour window and when you have already had unprotected sex or a birth control failure earlier in your menstrual cycle.

As Plan B only protects against one act of unprotected sex or birth control failure, having unprotected sex or birth control failure at another point in the same menstrual cycle can lead to pregnancy. Plan B may also be ineffective if you vomit within two hours of taking the pill.

Things happen and you may find yourself wondering if you could be pregnant after having unprotected sex. Plan B One-Step can drastically reduce your chances of pregnancy if taken correctly. However, if you miss your period and believe that you may be pregnant after taking Plan B, consult with your healthcare provider.


Liz Coyle

Liz is a Scottsdale-based writer and mom of two young children and one not so young Boston Terrier. She is a lover of cooking, travel, and any activities she can do with the kids. She loves to share her experiences of being a high-strung, type a mom in an imperfect world.

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