If the hCG levels are less than 1,200 mIU/ml (mili International Unit / mililiter), they can double in 48-72 hours. And if the levels are between 1,200 and 6,000 mIU/ml, they double in 72-96 hours. The hCG levels hit their peak during the initial weeks of your pregnancy, between the 8th and 11th week. However, as you move further in your pregnancy and reach the final trimester, the hCG levels in your body start to decline.