Human chorionic gonadotropin (hCG) is a hormone produced during pregnancy. Blood and urine tests detecting hCG are used to confirm pregnancy. However, hCG levels can also be monitored during pregnancy to check for potential issues like miscarriage or ectopic pregnancy. This article will explore how hCG testing works, how it can indicate miscarriage, and the limitations of using hCG to detect miscarriage.
What is hCG?
hCG stands for human chorionic gonadotropin. It is a hormone produced by the placenta shortly after fertilization occurs. Levels of hCG rise rapidly in the first trimester of pregnancy. This hormone serves to maintain the corpus luteum, which produces progesterone to support the pregnancy in early stages before the placenta takes over this function.
hCG can be detected in urine and blood. Urine and blood tests measuring hCG are used to confirm pregnancy, since it is only present when someone is pregnant. These hCG tests for pregnancy are highly accurate from the first day of a missed menstrual period.
How are hCG levels monitored in pregnancy?
Once pregnancy is established, hCG levels can be measured through blood tests to monitor the progress of the pregnancy. Doctors may recommend tracking hCG levels in the following situations:
- To check for potential miscarriage risk in early pregnancy
- To check for ectopic or tubal pregnancies
- To monitor pregnancies conceived through IVF or other fertility treatments
- To evaluate bleeding or spotting during pregnancy
In a normal pregnancy, hCG levels will roughly double every 48 to 72 hours through the first trimester. A slowed rise or decrease in hCG levels may indicate problems.
Typical hCG ranges during normal pregnancy:
| Weeks since last menstrual period | hCG levels (mIU/mL) |
|---|---|
| 3 to 4 weeks | 5 to 50 |
| 1 to 2 months (5 to 6 weeks) | 50 to 500 |
| 2 to 3 months (7 to 12 weeks) | 500 to 10,000 |
| 3 to 4 months (13 to 16 weeks) | 10,000 to 100,000 |
| 4 to 5 months (17 to 20 weeks) | 100,000 to 200,000 |
| 5 to 6 months (21 to 24 weeks) | 100,000 to 200,000 |
| 6 to 7 months (25 to 28 weeks) | 100,000 to 200,000 |
| 7 to 8 months (29 to 32 weeks) | 100,000 to 200,000 |
| 8 to 9 months (33 to 36 weeks) | 50,000 to 100,000 |
| 9 to 10 months (37 to 40 weeks) | 5,000 to 50,000 |
However, the exact hCG ranges can vary substantially between different pregnancies. The pattern of rising hCG levels is more relevant than the exact numbers.
How can hCG levels indicate a miscarriage?
Slow-rising or decreasing hCG levels can be an early indicator of a miscarriage or failed pregnancy. Reasons for abnormally rising hCG include:
- Non-viable pregnancy: The embryo failed to develop or growth stopped.
- Ectopic pregnancy: The embryo implanted outside the uterus and is not viable.
- Gestational trophoblastic disease: Abnormal placental tissue grows instead of a fetus.
- Blighted ovum: A gestational sac forms but no embryo develops.
- Impending miscarriage: The pregnancy is ending.
In some cases, levels may fail to rise normally right from the first positive pregnancy test. However, hCG levels can also seem normal at first before slowing and signaling trouble.
With a miscarriage, hCG levels usually peak and start dropping. Levels typically fall below 5 mIU/mL within 4 to 6 weeks after a pregnancy loss.
Patterns of hCG levels during miscarriage:
- Levels rise slower than expected or plateau.
- Levels rise appropriately at first, but then slow down or stall.
- Levels peak and start dropping before reaching the normal peak of 100,000 to 200,000 mIU/mL.
- Levels drop rapidly to zero rather than plateauing around 10,000 mIU/mL or more.
Falling hCG levels indicate the pregnancy is not viable. However, it takes time for hCG levels to completely clear after pregnancy loss. So even decreasing levels do not immediately confirm a miscarriage occurred. Doctors may measure hCG levels over several days to determine if a significant rise or fall is occurring.
Limitations of hCG for diagnosing miscarriage
While hCG trends provide insight, there are some limitations to using hCG alone to diagnose a miscarriage:
- A single hCG reading is not enough. Multiple tests are needed to identify slow rises or falls.
- Levels can fluctuate normally in early pregnancy, so patterns may not emerge until a later stage.
- Normal pregnancies can start with widely varying hCG levels.
- Other issues like ectopic pregnancy can produce similar hCG patterns to miscarriage.
- Even decreasing hCG does not guarantee a pregnancy loss has completed yet.
Ultrasound or other testing may be needed to fully assess the situation when hCG trends are abnormal. Doctors will also consider any symptoms the woman is experiencing when interpreting hCG test results.
Conclusion
In summary, hCG blood tests can provide an early warning of potential miscarriage when levels fail to rise normally. However, ultrasound and time for hCG levels to clear are still needed to confirm pregnancy loss occurred. hCG levels should be interpreted cautiously, as normal pregnancies can exhibit quite varied patterns. But when combined with other clinical information, tracking hCG levels can aid doctors in diagnosing miscarriage issues.