If you’re trying for a baby — or desperately trying to avoid getting pregnant — you’re likely wondering: How long after sex can you take a pregnancy test? While today’s new and improved home pregnancy tests offer results faster than ever before, inaccuracies can still occur if they’re not used properly.
“I used one of those early pregnancy tests with my daughter, and turns out, there’s such a thing as too early,” says Jennifer Higgins of New York. “I tested six days before my period was set to start — just like the box said — and got a negative result, even though I was, in fact, pregnant!”
From how soon after sex to take a pregnancy test (and the best time of day) to the reasons behind false negatives, here’s everything you need to know about taking a home pregnancy test.
How soon after sex can you take a pregnancy test?
When you’re worried about an unwanted pregnancy after unprotected sex (or contraception that went awry), it’s only natural to want to test as early as possible. But for the most accurate results, you want to wait at least 12 days after intercourse, or three weeks if you have an irregular period.
Pregnancy tests work by detecting the hormone human chorionic gonadotropin (hCG), which the body only begins producing after implantation (when a fertilized egg attaches itself to the lining of uterus). Typically, this occurs six to 12 days after you’ve ovulated.
“If you’re comfortable with the fact that you might get a false positive, you can take a home pregnancy test just 10 days after unprotected sex,” says Dr. Felice Gersh, a board-certified OB-GYN. “Sometimes pregnancy tests will turn positive by then. But keep in mind, that still is on the early side.”
“If you’re comfortable with the fact that you might get a false positive, you can take a home pregnancy test just 10 days after unprotected sex.”
DR. FELICE GERSH, OB-GYN
When to take a pregnancy test during your cycle
Even though some early pregnancy tests claim to be able to detect hCG over a week before menstruation is supposed to begin, you should proceed with caution when testing before your period is due.
“A woman can run a pregnancy test on herself at any time in her cycle, but it’s accuracy is always dependent on the quantity of hCG that’s present in the urine,” says Gersh. “In other words, if you’re pregnant and test too early, it can give you a negative result. Waiting an additional week after a missed period to test will substantially reduce the chance of a false negative.”
When is the best time of day to take a pregnancy test?
Although late-night, panic-induced drugstore runs aren’t unheard of when it comes to pregnancy tests, it’s best to wait until morning.
“Home pregnancy tests are best taken right after waking up, since that’s when the concentration of hCG is highest in the urine,” says Dr. Kecia Gaither, an OB-GYN, maternal fetal specialist, and the director of perinatal services at NYC Health and Hospitals in New York.
To increase the accuracy, Gersh advises waiting to drink any fluids until after you’ve taken the test.
Causes of a false negative pregnancy test
In addition to testing too early in your cycle, other potential causes for false negatives are:
- Checking the test too quickly. (Follow test directions to a T!)
- Using urine that’s too diluted and therefore lacking the amount of hCG required for detection.
It’s also important to keep in mind that while home pregnancy tests are just as accurate as the urine tests you get in the doctor’s office, they’re not as effective if they’re expired. Always check the expiration date before taking a pregnancy test to make sure it’s up-to-date.
Causes of a false positive pregnancy test
While too-early testing can result in a false negative, it’s “very, very rare” to get a false positive, according to Gersh.
However, false positives aren’t completely unheard of. Here are a few causes:
- Early miscarriage. Chemical pregnancies, which are when pregnancy is lost shortly after implantation, may result in a “false” positive — even though, technically-speaking, the test was initially accurate.
- Residual hCG. If you’ve recently given birth or had a miscarriage, there may still be hCG in your system. One German study found that hCG levels should return to normal three weeks postpartum.
- Age. A study published in the journal PLoS One found that “false positive results increase with age due to increases in pituitary hCG during and after menopause.” According to the Mayo Clinic, the average age for menopause in the U.S. is 51, but it can happen in your 40s or 50s.
- Medications. If you’re taking fertility medications that increase hCG levels, such as injections as part of your in vitro process, a false positive could happen — particularly if you test shortly after receiving one.
- Evaporation lines. When using a test where two lines indicate a positive, it’s especially important to check results within the instructed time frame. With some tests (and depending on the chemical composition of some urine samples), a very faint “evaporation line” can form when a test has been left out for a prolonged period of time and the urine has completely dried.
What does a faint line on a pregnancy test mean?
If you’re straining to make out what appears to be a faint line on your pregnancy test, there’s a good chance you’re pregnant.
“Faint lines are generally indicative of a very early pregnancy,” says Gaither.
If you were inclined to take another test a few days later — just to be sure — you wouldn’t be alone.
“With my first pregnancy, the line was super-faint when I first tested, so I wasn’t sure if it counted as a positive,” says Krysten Mace, of Cranford, New Jersey. “Sure enough, though, when I tested the following day, that second line was unmistakable.”
How accurate are pregnancy tests?
As long as it’s not expired, and it’s being used the proper way (at the proper time), home pregnancy tests are about 97% accurate.
“The drugstore urine pregnancy tests are just as effective as the ones taken in your physician’s office,” says Gaither.
“The drugstore urine pregnancy tests are just as effective as the ones taken in your physician’s office.”
DR. KECIA GAITHER, OB-GYN
That said, you can have a blood pregnancy test done at your doctor’s office, which can detect hCG earlier than a urine test. Depending on whether or not there’s a lab on-site, results can take anywhere from a few hours to a few days.
Signs you may be pregnant
If you haven’t gotten your period and are experiencing any of the following early pregnancy symptoms, you may want to take a pregnancy test:
- Nausea and/or food aversions.
- Constipation.
- Fatigue.
- Breast tenderness.
- Vaginal spotting.
- Abdominal cramping.
- Moodiness.
- Headaches.
If the test is negative and you still haven’t gotten your period, keep in mind there are a number of factors besides pregnancy that can contribute to a late period or irregular cycle, including:
- Breastfeeding.
- Stress.
- Extreme weight loss or weight gain.
- Illness.
- Travel.
- Starting or stopping birth control pills.
- Perimenopause.
Additional health conditions that may cause a late period include:
- Premature ovarian failure. Also known as primary ovarian insufficiency, premature ovarian failure happens when the normal functioning of ovaries is disrupted before age 40.
- Polycystic ovarian syndrome (PCOS). A common endocrine system disorder that’s caused by an imbalance of reproductive hormones. While treatable, PCOS can cause sporadic or irregular periods.
- Pelvic inflammatory disease (PID). Occasionally a symptom of PID, which is an infection of the reproductive organs caused by a sexually transmitted disease, is irregular periods.
Whether you’re hoping to be pregnant or not, having a late period can be nerve-wracking. Thankfully, home pregnancy tests can offer quick answers without a trip to the doctor when used properly. That said, if you’re unsure about your results or have questions, it’s always smart to speak with your health care provider.
