They look for the HCG human in your urine, and based on how much of that hormone is found, the darker the line turns.

We've consulted maternity health experts as well as Mumsnet users - the largest online network of mums in the UK - to help narrow down a shortlist of the best pregnancy tests currently available, from those you can use up to six days before a missed period to others which give you your answer in just 45 seconds.It is designed for emergencies and not regular use and requires you to have add a recent asthma review. Which may be particularly welcome if you are positive as, as all the best parenting books will warn you, babies don't come cheap! Many Mumsnetters swear by the First Response Early Result Pregnancy Test as the most accurate pregnancy test.

Although you can use this test up to 5 days before your expected period, your test may be less effective the earlier you test. If you find this a bit tricky you can always take a urine sample and dip the tip into this instead – the results will be the same. All our General sales List (GSL) products are dispensed by MHRA premises number WDA (H) 1411 and all Pharmacy only Medicine(P) products are dispensed by Pharmacy Premises number 9011577. This product is First Response’s best selling pregnancy test and has been voted Best Pregnancy Test for 2 years in a row by trusted pregnancy and parenting brand. The first few weeks of pregnancy are critical to fetal development, so early prenatal care is important for a healthy birth weight and the baby’s survival.This rises to 99% accuracy the day after your missed period, making it similar to the Clearblue Digital Test With Weeks Indicator in terms of early-testing accuracy, but without the cost. The First Response Early Result Pregnancy Test is a pregnancy test which can tell you whether or not you’re pregnant as early as 6 days before your missed period. It is designed to detect pregnancy hormones in your urine, providing you with accurate results in just a few minutes. Again, it reveals the result in words rather than two lines, which some women find easier to interpret. Although this early pregnancy test can be used up to 4 days before your period is due, it’s important to note that the test only offers a 53% accuracy this early, barely better than 50:50.