Human chorionic gonadotropin (HCG) is a hormone produced during pregnancy, often referred to as the “pregnancy hormone.” Its presence is what pregnancy tests detect to confirm a pregnancy. Following a miscarriage, the body naturally begins to reduce its production of HCG, causing levels to decline.
Understanding HCG and Miscarriage
HCG is produced by the placenta, which develops in the uterus during pregnancy to provide nutrients and oxygen to the fetus. This hormone plays a role in supporting the early stages of pregnancy. Medical professionals monitor HCG levels through blood tests in early pregnancy to assess its progression. A rapid rise in HCG levels is expected in a viable pregnancy, often doubling every 2 to 3 days in the first four weeks.
If HCG levels show a slow rise or begin to decline, it can indicate a miscarriage or a nonviable pregnancy. After a miscarriage, the body ceases HCG production as the pregnancy tissue is no longer present. HCG levels are expected to fall, eventually returning to pre-pregnancy levels.
Factors Influencing HCG Decline
The rate at which HCG levels decrease after a miscarriage is influenced by several factors. The initial HCG level at the time of the miscarriage is a factor; higher concentrations mean it will take longer for the hormone to clear.
Gestational age also plays a role. Early miscarriages, when HCG levels are lower, typically see a quicker decline compared to later first-trimester miscarriages, when HCG levels are much higher. The method of miscarriage management (spontaneous, medically induced, or surgically managed like a D&C) can also affect the rate of HCG decline.
Typical Timeline for HCG to Return to Normal
After a miscarriage, HCG levels gradually decrease, aiming to return to a non-pregnant baseline, defined as below 5 mIU/mL. The time to reach this level varies significantly, from a few days for very early losses to several weeks or even a couple of months, especially if initial HCG levels were very high. A study in 2013 observed a 35% to 50% reduction in HCG levels two days after a miscarriage, and a 66% to 87% reduction after seven days.
Home pregnancy tests detect HCG in urine and can remain positive for a week to several weeks after a miscarriage due to their sensitivity, until HCG drops sufficiently. This is why a positive home pregnancy test does not necessarily indicate a new pregnancy or retained tissue immediately after a loss.
When HCG Levels Don’t Decline
If HCG levels do not decline as expected or rise after a miscarriage, medical evaluation is warranted. One common reason for persistently elevated HCG is retained pregnancy tissue (RPOC), where placental or fetal tissue remains in the uterus, continuing to produce HCG.
A molar pregnancy is a rare but serious complication where abnormal tissue grows in the uterus instead of a healthy pregnancy. This abnormal tissue can produce very high HCG levels, sometimes exceeding 100,000 mIU/mL, which may not decline appropriately after a miscarriage. Another possibility is a new conception before HCG from the previous pregnancy has fully cleared, leading to rising HCG levels. Ectopic pregnancies, where the fertilized egg implants outside the uterus, can also lead to HCG levels that do not decline as expected or rise slowly.
Importance of Follow-Up and Monitoring
Medical follow-up after a miscarriage is important to ensure complete resolution and identify potential complications. Healthcare providers often use serial HCG blood tests to monitor the hormone’s decline, confirming all pregnancy tissue has passed. For example, HCG levels may be measured weekly until they fall below 5 mIU/mL.
Consistent monitoring confirms the miscarriage is complete and rules out issues like retained tissue or a molar pregnancy. Open communication with medical professionals about any concerns or persistent symptoms after a miscarriage is always advised.