Twin: One of two children produced in the same pregnancy. Twins can develop from one ovum (egg) or from two ova (eggs). Twins who develop from a single ovum are called monozygotic or identical twins. They have identical genomes. Twins who develop from two ova that are fertilized at the same time are called dizygotic or fraternal twins. They are nonidentical and have different genomes.
Unfortunately, many women have a small amount of this hormone continuously and if the level gets high enough just before a period, you could get a false pregnancy test result. The best time to use a urine test for pregnancy is three to five days after your missed period.
One of the most common reasons for a false negative result is testing too early. In order for a pregnancy test to show accurate results, you have to give your body time to produce the levels of hcg (pregnancy hormone) that the pregnancy test needs in order to trigger a positive result.