When a fertilized egg adheres to the lining of your uterus and pregnancy starts, HCG is produced. If your pregnancy test comes back positive, it signifies you're expecting a child. If they are negative, you are not pregnant. When you take a pregnancy test after you've missed your period, it's the most accurate. Pregnancy tests detect the presence of HCG in your urine. They work by using antibodies that bind to specific parts of HCG. The result is a pink line if you are pregnant or a white line if you are not. HCG can be found in both men and women who are pregnant. It is the single most reliable indicator of pregnancy status. Women's bodies produce small amounts of HCG throughout their pregnancies, so a blood test or urine test cannot determine whether you are actually pregnant. Only a pregnancy test can do that. HCG levels also remain high after you give birth, which is why post-partum depression is often called "the baby blues." Healthy women without any signs of pregnancy will usually only have trace amounts of HCG in their blood. This level increases as you go into your second trimester and reaches its highest point during the third trimester. A blood test can tell us how far along you are in pregnancy and may indicate any problems with your pregnancy. A doctor will know how to read these results once you've had your baby.