A pregnancy test with one dark and one light indicates a high chance of pregnancy, but confirmation of pregnancy requires a blood test for HCG levels and a pelvic ultrasound.
The pregnancy test measures human chorionic gonadotropin, or HCG, in the urine, which is elevated in a woman’s body when a fertilized egg is implanted and develops, and can be found in the blood and urine.
If the concentration of HCG in the urine reaches a certain level, the pregnancy test will show two bars, one dark and one light is a weak positive, the chances of pregnancy are very high.
However, there is a possibility of false positives or false negatives in pregnancy tests. To be sure of pregnancy, you need to go to the hospital to have your blood HCG level tested, and you need to have a pelvic ultrasound to determine whether the pregnancy is normal intrauterine pregnancy, in order to rule out ectopic pregnancy, biochemical pregnancy, gravida and other abnormalities.