Pregnancy Test Accuracy Four Days Before Expected Period

Lou asked

As per our conversation, I missed one combined hormone. It was the second one in the pack. I did a pregnancy test today (4 days before the expected period). I had a negative result. Would this be accurate? Or should I still be worried?

Answer

As discussed in one of our previous answers, while missing one dose of your birth control pills in the first week isn't ideal, it likely won't decrease their effectiveness that much.

In fact, most sources, such as the Centers for Disease Control, state that emergency contraception generally isn't needed after one missed dose. They simply recommend to:

• Take your missed dose as soon as you remember.
• Take the next pill at your regular time. This means you may take two pills in one day.
• You do not need to use a back-up birth control method if you have sex.

Having said all that, it's never a bad idea to take a pregnancy test after a month in which there may have been a problem taking your pills. Pregnancy isn't likely in your situation but ruling it out can certainly bring peace of mind.

Data vary widely in regard to how accurate a pregnancy test is 4 days prior to your period. Some studies indicate an accuracy rate of around 50% while some products claim nearly 96% accuracy. This is discussed more below.

Pregnancy Test Accuracy

A key factor in the accuracy of pregnancy tests is the particular product you are using to test since they all have different sensitivities for hCG (human chorionic gonadotropin), the hormone present in urine after an egg is fertilized.

The accuracy of pregnancy tests increases as you get closer to the date of your expected period. The more days before your expected period you test, the less accurate the test becomes.

For example, testing on the day of your expected period will be far more accurate than testing 5 days before your expected period.

There have been some studies discussing how accurate pregnancy tests are in regard to when the test was taken. One found the following results:

• 52% accurate three days before a missed period.
• 69% accurate two days before a missed period.
• 86% accurate one day before a missed period.
• Over 95% accurate on the day or missed period or after.

As mentioned above, over the counter pregnancy tests have different sensitivity levels for hCG, which of course alters how soon they can detect pregnancy.

Additionally, some products test for different forms of hCG, such as hCG-h and beta-hCG. They may be able to produce a positive result more than 3 days before a missed period.

One such product is the First Response Early Result test. They give the following numbers on their website:

In laboratory testing, FIRST RESPONSE™ detected the pregnancy hormone levels in 76% of pregnant women, 5 days before their expected period; in 96% of pregnant women, 4 days before their expected period; in >99% of pregnant women, 3 days before their expected period; in >99% of pregnant women, 2 days before their expected period; in >99% of pregnant women, 1 day before their expected period; and in >99% of pregnant women, on the day of their expected period."

While these are pretty strong numbers, it is important to note that there is significant variability among individuals that could affect these results.

Some pregnant women may not have detectable amounts of hormones in the urine when they test, even on the day of their expected period.

In fact, one study found almost 10% of women don't produce enough hCG to be detected until a week or so after a missed period.

Lastly, there are many studies which are dubious of the claimed detection times for many over the counter home pregnancy tests. One study concluded the following:

"Universal claims for OTC-PTs [Over The Counter pregnancy tests] of more than 99% laboratory accuracy and use as early as the first day of missed period, while cleared for use by the U.S. Food and Drug Administration, are ambiguous and inappropriate for many products, according to these data. The majority of products tested were found to detect only a small percentage of pregnancies on the first day of a missed menstrual period. Until more data become available on the actual clinical sensitivity of these products, pharmacists should advise consumers to be cautious in interpreting test results."

So, to answer your question specifically regarding testing four days prior to your expected period, a home pregnancy may be able to detect levels of hormone indicating pregnancy that early, but testing closer to, or after, your expected period will be far more accurate.

Going to your doctor for a pregnancy test is the best way to know for sure.