Human chorionic gonadotropin (HCG) plays a key role in early gestation. After a miscarriage, understanding how HCG levels decline provides important information about the body’s recovery.
Understanding HCG and Miscarriage
HCG is a hormone produced by the placenta after a fertilized egg implants. It supports the corpus luteum, which produces progesterone to sustain early pregnancy. HCG levels typically rise rapidly, often doubling every 48 to 72 hours, peaking around 8 to 11 weeks of gestation before gradually declining.
A miscarriage is the spontaneous loss of a pregnancy before 20 weeks, with most occurring in the first trimester. When a pregnancy ends, the body no longer produces HCG to support it.
The HCG Drop Timeline
After a miscarriage, HCG levels decline as the body no longer needs to support the pregnancy. The rate varies, typically taking days to several weeks to return to a non-pregnant state. For a complete miscarriage, HCG levels may decrease by 35% to 50% within two days and 66% to 87% within seven days.
Several factors influence this timeline. The gestational age at the time of the miscarriage is a significant determinant. Earlier miscarriages, with lower initial HCG levels, generally see a quicker return to baseline. Conversely, later miscarriages, when HCG levels are higher, may take longer to become undetectable.
The completeness of the miscarriage also affects the decline rate. In a complete miscarriage, where all pregnancy tissue has been expelled, HCG levels drop more consistently. If the miscarriage is incomplete, with some tissue remaining, the HCG decline may be slower. Individual variations in metabolism also contribute to how quickly the body processes and eliminates HCG.
Monitoring HCG Levels and What to Expect
Healthcare providers monitor HCG levels after a miscarriage to ensure they are declining appropriately. This is typically done through quantitative blood tests, which measure the exact amount of HCG in milli-international units per milliliter (mIU/mL).
A “negative” HCG level is generally considered below 5 mIU/mL. Levels must reach this baseline to confirm all pregnancy tissue has been expelled and the body is returning to a non-pregnant state. While blood tests are more accurate, individuals often wonder when a home pregnancy test will become negative.
Home pregnancy tests are less sensitive than blood tests, often requiring HCG levels above 20 mIU/mL for a positive result. Due to residual HCG, a home pregnancy test can remain positive for days to weeks after a miscarriage, even as blood levels fall. The exact time until a negative home test varies based on the initial HCG level and decline rate.
When HCG Levels Don’t Decline as Expected
HCG levels may not decline as anticipated after a miscarriage, requiring further medical evaluation. One common reason for persistent or slowly declining HCG is retained placental tissue, also known as retained products of conception (RPOC). This tissue can continue to produce HCG, preventing levels from returning to baseline.
Another possibility for elevated HCG is a new, very early pregnancy. It is possible to conceive again before menstruation resumes, leading to rising HCG levels from a new pregnancy. A rare but serious cause for HCG not declining is gestational trophoblastic disease (GTD), which includes conditions like a molar pregnancy.
GTD involves abnormal growth of cells that would normally form the placenta, producing high levels of HCG. In these cases, HCG levels may remain elevated, plateau, or even rise, necessitating specific treatments. If HCG levels do not fall as expected, or if symptoms like continued bleeding or pain are present, consult a healthcare provider for proper diagnosis and management.