text: The Doubling Rule.\nDoctors can also perform quantitative serum beta hCG levels. The measurement is done in mIU/ml, and a level above 25 mIU/ml usually indicates the presence of a pregnancy. Two tests are usually necessary to verify a normal increase, usually 2-3 days apart. The increase in serum hCG can be interactively monitored. Below an hCG level of 1,200 mIU/ml the hCG usually doubles every 48-72 hours, though a rise of 50-60% is still considered normal. Between 1,200 and 6,000 mIU/ml serum the hCG usually takes 72-96 hours to double, and above 6,000 mIU/ml, the hCG often takes more than four days to double. Failure to increase normally may indicate that the pregnancy is not developing well and can be an early sign for a possible miscarriage or an ectopic pregnancy.