Expert Answers Factual Answers to Your Sexual Health Questions

anonymous on August 30, 2011

How long do I need to wait after sex to take a pregnancy test?

After having unprotected sex, how long should I wait before I can check whether I’m pregnant? What’s the best way to test for pregnancy?

answered by Lisa Oldson, MD on August 30, 2011

Thanks for your sharing your question. Whether you’re trying to get pregnant or you’re worried about an unintended pregnancy, knowing your status as early as possible is helpful.

According to the U.S. Department of Health and Human Services Office on Women’s Health,  it’s best to wait one week after you miss your period for the most accurate pregnancy test results. Why? It takes that long for a unique pregnancy chemical to build up in the body.

Let me explain further...

Pregnancy tests look for a specific chemical that the body begins to make as soon as a fertilized egg implants in the uterus. But after an egg has been fertilized, it takes 6-9 days for the embryo to implant. Then it takes another week for the body to build up enough of the chemical (called human chorionic gonadotropin or hCG) to register on a pregnancy test. In other words, it takes about 2-3 weeks after ovulation for the chemical to show up in the body, or about one week after a woman should have gotten her period.

Now let’s talk about the types of tests available for women who think they might be pregnant...

There are two types of tests women can take to find out if they’re pregnant...a blood test or a urine test. A blood test is more sensitive than a urine test and needs to be done by a doctor. A urine test can be done by a doctor or using an at-home pregnancy test.

Many women prefer the convenience of taking a pregnancy test at home before visiting the doctor for confirmation. At-home pregnancy tests looks for hCG and they can give relatively accurate results if done according to instructions. However, it’s always a good idea to read the packaging because different at-home tests have different sensitivities. Some early response tests can provide an accurate result on the first day of a missed period. Others will provide the most accurate result one week after a missed period.

If you find out that you’re pregnant, make an appointment with your doctor. Therea doctor can help you learn about how to care for yourself and plan during pregnancy. Or, if you don’t want to have a baby, talking with a doctor can help clarify your options.

I hope this information was helpful to you, and I wish you good luck and good health.

Related info:

Lisa Oldson, MD

Dr. Oldson is Medical Director of the Analyte Physicians Group. She is on staff at Northwestern Memorial Hospital, as well as Clinical Instructor at the Feinberg School of Medicine, Northwestern University. Her areas of expertise include STDs (with a particular clinical emphasis on herpes), women's health, preventive medicine, diabetes, obesity and weight management, and mood and anxiety disorders. Dr. Oldson was educated at Rush Medical College and completed her residency at Rush-Presbyterian-St. Luke's Medical Center in Chicago, IL.

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