Human Chorionic Gonadotropin (HCG) is a glycoprotein hormone produced by the trophoblast cells, which are the precursors to the placenta. This hormone is detected by both at-home urine tests and laboratory blood tests to confirm pregnancy. HCG’s main function is to signal the body to maintain the corpus luteum, a temporary structure in the ovary. The corpus luteum then produces the progesterone necessary to support the uterine lining and sustain the early stages of gestation. HCG level changes serve as a biological marker reflecting the health and progression of a pregnancy.
The Natural Decline During Healthy Pregnancy
HCG levels in a viable pregnancy rapidly increase, doubling roughly every 48 to 72 hours during the first few weeks after implantation. This rapid rise indicates a healthy, progressing early pregnancy. Levels continue to climb until they peak, usually between the 8th and 12th week of gestation.
Peak levels vary widely, commonly falling between 25,000 and 300,000 mIU/mL. Following this peak, HCG levels begin a natural and steady decline over several weeks. The concentration then settles at a significantly lower plateau, often representing only 10% to 20% of the maximum level, which is maintained until delivery.
HCG Clearance Following Delivery or Termination
Once the source of the hormone (the placenta) is removed after delivery, miscarriage, or termination, HCG begins to clear from the bloodstream. The hormone is metabolized primarily by the liver and kidneys, following a biphasic pattern. The initial decline is rapid, with a half-life of approximately 9 to 31 hours during the first few days. This is followed by a much slower phase of elimination, where the half-life extends to between 55 and 64 hours.
The total time required for HCG to return to non-pregnant levels (less than 5 mIU/mL) is highly variable. For a full-term pregnancy, this process typically takes around four to six weeks postpartum. Clearance time depends heavily on the maximum HCG level reached; pregnancies that ended earlier generally see a faster return to baseline, often within two to four weeks.
Monitoring HCG Decline After Pregnancy Loss
When a pregnancy is non-viable, such as with a miscarriage or ectopic pregnancy, providers monitor HCG decline to confirm complete resolution. After a spontaneous miscarriage, the expected rate of decline is a drop of approximately 21% to 35% within the first two days, and 60% to 84% at seven days.
An abnormally slow decline or a plateau can signal retained products of conception or a persistent ectopic pregnancy. In these cases, medical intervention, such as medication or surgery, may be necessary.
Monitoring is prolonged and important in the case of a molar pregnancy, where abnormal tissue growth results in very high HCG levels. Surveillance continues until HCG levels remain undetectable for a specific period, often six to twelve months, to ensure the abnormal cells have resolved. A plateauing or rising HCG level during this time may indicate the development of gestational trophoblastic neoplasia, requiring specific treatment.