The article is professionally consulted by Specialist Level I Doctor Nguyen Thi Man – Department of Obstetrics and Gynecology, Vinmec Da Nang International Hospital. Dr. Man has over 10 years of experience in diagnosing, consulting, and treating in the field of Obstetrics and Gynecology.
Human Chorionic Gonadotropin (hCG) is a hormone produced during pregnancy, playing a pivotal role in fetal development. Due to its rapid increase following conception, hCG testing is commonly used for early pregnancy detection and monitoring the pregnancy's progress.
1. What is hCG hormone?
hCG stands for Human Chorionic Gonadotropin, a sialoglycoprotein hormone with a molecular weight of approximately 46,000 daltons. It comprises two subunits: alpha and beta. The beta subunit is unique to hCG, while the alpha subunit shares an amino acid sequence with several other hormones in the body.
hCG is synthesized by placental trophoblast cells and plays a critical role in sustaining the embryo. It stimulates the production of estrogen and progesterone, which thicken the uterine lining and enhance blood supply for fetal development. Furthermore, hCG signals the brain to temporarily halt the menstrual cycle.
Monitoring hCG levels not only aids in early pregnancy detection but also helps track the ongoing status of the pregnancy.
2. Changes in hCG Levels During Pregnancy
In women with normal health who are not pregnant, hCG levels are typically below 5mUI/ml. For pregnant women, hCG levels will be higher than 25mUI/ml. If hCG levels are between 6-24mUI/ml, pregnancy status cannot be determined and further monitoring is required. After childbirth or miscarriage, hCG levels will return to normal (< 5mUI/ml) within 4-6 weeks.
hCG is produced very early, right after the fertilized egg implants into the uterine lining. In early pregnancy, hCG levels in the blood are relatively low but increase rapidly, usually doubling every 48-72 hours. hCG levels peak between weeks 8 and 11 of pregnancy, then gradually decrease and stabilize for the remainder of the pregnancy. hCG levels vary according to gestational age as follows:
| 3 weeks | 5-50 mUI/ml | 9-12 weeks | 25700-288000 mUI/ml |
| 4 weeks | 5-426 mUI/ml | 13-16 weeks | 13300-254000 mUI/ml |
| 5 weeks | 18-7340 mUI/ml | 17-24 weeks | 4060-165400 mUI/ml |
| 6 weeks | 1080- 56.500 mUI/ml | 25 weeks to delivery | 3.640-117.000 mUI/ml |
| 7-8 weeks | 7650-229000 mUI/ml | 4-6 weeks postpartum | <5mUI/ml |
hCG levels vary widely among pregnant women and can change significantly throughout the pregnancy. The important aspect to note is whether the hCG levels fall within the common average range and whether the increase and decrease in hCG levels follow the physiological pattern for each stage of pregnancy.
When hCG levels are excessively high or low compared to the usual physiological curve, it may indicate abnormalities in the pregnancy. Low hCG levels could suggest the possibility of miscarriage, stillbirth, or ectopic pregnancy. Excessively high hCG levels could indicate conditions such as placental diseases, molar pregnancies, trophoblastic diseases, or multiple pregnancies.
3. Is the Beta hCG Level Different for Twin Pregnancies Compared to Single Pregnancies?
Women carrying twins generally have higher hCG levels compared to those with single pregnancies; the beta hCG test results for twins are usually 30-50% higher than for single pregnancies. However, this difference is not clear until the end of the early pregnancy stage.
The variation in hCG levels among pregnant women and in the same woman at different times of pregnancy is significant. There is no specific number for hCG levels at any given time, usually, there is a range. Therefore, beta hCG test results should not be used to diagnose twin pregnancies due to low accuracy.
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