ASK YOUR HCG QUESTIONS HERE. In most normal pregnancies at hCG levels below 1,200 mIU/ml the hCG usually doubles every 48-72 hours. At levels below 6,000 mIU/ml the hCG levels normally increase by at least 60% every 2-3 days, though increases between 50-60% can sometimes still be seen in normal pregnancies.SK YOUR HCG QUESTIONS HERE. In most normal pregnancies at hCG levels below 1,200 mIU/ml the hCG usually doubles every 48-72 hours. At levels below 6,000 mIU/ml the hCG levels normally increase by at least 60% every 2-3 days, though increases between 50-60% can sometimes still be seen in normal pregnancies.