A home pregnancy test works by measuring the level of human chorionic gonadotropin (HCG) in your urine. This pregnancy hormone is secreted by the developing placenta shortly after fertilization occurs. Under laboratory conditions, home pregnancy test accuracy is about 99%. However, this assumes that you have followed the test instructions correctly and not done anything to damage the test kit.
False Positives and False Negatives
When discussing home pregnancy test accuracy rates, it's important to understand the difference between a false positive and a false negative result. A false positive result would indicate that you are pregnant when conception has not actually occurred. A false negative result would indicate that you are not pregnant when you really are.
Generally, false negative results are more common than false positive results. Most false negative results are caused by user error, while false positives are more often attributed to a chemical pregnancy, interference caused by certain fertility medications, or other rare medical conditions.
Accuracy and Test Sensitivity
If you're concerned about home pregnancy test accuracy, you may want to purchase a test that has a higher sensitivity to detect HCG levels earlier in your pregnancy.
Typically, HCG levels are measured in milliInternational Units (mIU) or amounts equal to 1/1000th of an IU per milliliter. This means a home pregnancy test with a sensitivity of 20 mIU/ml is more sensitive than a test with 50 to 100 mIU/ml.
A 20 to 25 mIU/ml test allows for earlier detection of pregnancy, possibly as soon as eight days after conception. However, it's important to remember that conception may take place several days after date of intercourse. Do not use the date of sexual intercourse as the day of conception when determining which test you should purchase.
Tips for Improving Pregnancy Test Accuracy
The following tips will help with accuracy as you're completing the test:
- Wait until your period is at least one week late, particularly if you've had irregular menstrual cycles in the past. Testing on the first day of your missed period results in pregnancy test accuracy rates of about 80%.
- Store your test at the proper temperature and never leave it in a hot car. Extreme heat or cold can damage your home pregnancy test.
- Follow the test's timing instructions. Waiting too long to read the results or reading the results before the specified time period has passed can cause a false positive or false negative result.
- Take the test right away in the morning, when your pregnancy hormone levels should be the highest.
- Don't consume large amounts of coffee, soda, water, or other beverages before the test. This can affect the levels of HCG in your urine.
- If you don't understand how to take your home pregnancy test, call the customer service number listed in the instruction pamphlet for further assistance.
- Never use a test that has passed its expiration date.