In normal subjects, hCG in urine provides an early indication of pregnancy. Human chorionic gonadotropin (hCG) is produced by trophoblastic tissue and appears around 8-9 days after ovulation where fertilization has occurred, or around 4 days after conception. In a 28 day cycle with ovulation occurring at day 14, hCG can be detected in urine or serum in minute quantities around day 23, or 5 days before the expected menstruation. The hormone concentration doubles approximately every 2 days and peaks between 7-12 weeks after the first day of the last menstrual period with a mean concentration of 50,000 mIU/mL. Since elevated hCG levels are also associated with trophoblastic disease and certain nontrophoblastic neoplasms, the possibility of having these diseases must be eliminated before a diagnosis of pregnancy can be made.
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