Find out how reliable home pregnancy tests are and what complications can cause false positive or false negative pregnancy test results.
Home pregnancy tests are accurate as long as you follow the instructions correctly.
A positive test result is almost certainly correct. However, a negative test result is less reliable. The result may not be reliable if you:
- don't follow the instructions properly
- take the test too early
Some medications can also affect the results.
Carrying out a test
When you become pregnant, your body produces the pregnancy hormone, human chorionic gonadotrophin (HCG). Home pregnancy tests detect HCG in your urine.
You can take most pregnancy tests from the first day of your missed period. Tests carried out earlier than this are not always accurate. For more information, see How soon can I do a pregnancy test?
Check the instructions to make sure you can do the test at any time of day. It's usually best to take the test first thing in the morning as your urine will have the highest concentration of hormones at this time.
Avoid drinking too much fluid beforehand, as this can dilute the level of HCG in your urine.
Positive test results
If the test result is positive, you're almost certainly pregnant. Contact your GP surgery as soon as possible. Because home pregnancy tests are so accurate, your GP may not repeat the test.
If you want to continue with your pregnancy, it's a good idea to start your antenatal care as soon as possible. If you're not sure whether you want to continue with the pregnancy, you can find more information about your options here: Am I pregnant?
If you want to know when the baby is due, you can use our pregnancy due date calculator.
Negative test results
If the test result is negative, you may not be pregnant. However, negative results are less reliable. For example, if you do a pregnancy test too early, you could be pregnant, but there may not be enough HCG in your body to give a positive test result.
Pregnancy tests vary in their sensitivity (how soon they can detect HCG and what level of HCG needs to be present). You can find information on the packaging about how sensitive your test is.
If you still think you're pregnant after a negative result, wait a few days and try again. Speak to your GP if you get a negative result after a second test but your period hasn't arrived.
Some medications can affect test results, including:
- promethazine – used to treat conditions such as allergies
- medicines used to treat Parkinson's disease
- sleeping tablets (hypnotics)
- diuretics (medicines that increase the amount of urine produced) – used to treat conditions such as heart failure
- anticonvulsants (medicines that prevent seizures or fits) – used to treat conditions such as epilepsy
- medicines used for infertility
If you're taking any medication, the patient information leaflet that comes with it will tell you if it affects test results. You can also ask a pharmacist.
If your first pregnancy test result is positive, but a later one is negative or your period arrives, it's possible you've had an early miscarriage. Speak to your GP or midwife for advice.