hCG, or human chorionic gonadotropin, is a hormone your body produces during pregnancy. Once the implantation occurs, this is the first hormone that appears, and this is the main hormone needed to confirm the pregnancy. 

What do hCG levels look like?

There’s a steep increase in your hCG level during pregnancy, doubling every 48 to 72 hours in the first few weeks, reaching its highest point around 8-12 weeks of gestation. There is a wide range of what is deemed "normal" because these levels can differ greatly from person to person.

To give you a general idea: 

hCG levels are vital to confirm the pregnancy, monitor the early development, and to check for miscarriage or an ectopic pregnancy.