A human chorionic gonadotropin (HCG) test is done to check for the presence of HCG in blood or urine. The hormone is produced in the early stages of pregnancy (as early as ten days after conception). Generally, blood tests are more sensitive than urine tests and can therefore be done earlier with the same level of accuracy. If the first test result is negative but a pregnancy is still suspected, the test should be retaken about a week later. Because HCG rises rapidly, a negative result can turn positive within this time period.