It is best to use morning urine for early pregnancy test because the HCG concentration in urine is relatively low when you are newly pregnant, so if you use the urine at noon or at night, the possibility of a positive test is relatively low. The concentration of HCG in morning urine is higher than that in urine at other times, so the probability of a positive test using morning urine is higher. As the pregnancy continues, for example, when you are more than 40 days pregnant, the positive rate will increase whether you use morning urine, noon urine, or evening urine for testing, because the HCG concentration will gradually increase as the pregnancy progresses, so a positive result will occur whenever the urine is used for testing.