In early pregnancy the syncytiotrophoblast cells of the placenta release human chorionic gonadotropin (hCG) which serves as an essential hormone. This hormone functions as an essential element for sustaining pregnancy while also offering diagnostic capabilities and enabling the evaluation of pregnancy outcomes. Human chorionic gonadotropin produces several significant physiological changes as its primary function.
Maintaining Corpus Luteum Function
The most important function of hCG is to stimulate the corpus luteum of the ovary to continuously secrete progesterone (progesterone) and estrogen in early pregnancy. In a normal menstrual cycle, if there is no fertilization, the corpus luteum will degenerate; but during pregnancy, hCG can prevent the corpus luteum from degenerating and transform into a corpus luteum of pregnancy, maintain the endometrium, and facilitate embryo implantation and development.
Promote Formation and Function Maintenance of Placenta
hCG promotes the formation of the placenta and maintains its endocrine function until the placenta itself can secrete enough estrogen and progesterone.
Promote Development of Testicular Interstitial Cells (Male Fetus)
In male fetuses, hCG can stimulate testicular interstitial cells (Leydig cells) to secrete testosterone, which is essential for the development of male sexual organs.
Participate in Immune Regulation Function
hCG may help maintain pregnancy by regulating the maternal immune system and reducing the rejection of the embryo.
Promote Synthesis of Other Placental Hormones
hCG can stimulate the placenta to synthesize other hormones such as placental lactogen (hPL), and participate in various physiological regulation processes of pregnancy.
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hCG Introduction
- Source: Produced by embryonic trophoblast cells, and continuously secreted by the syncytiotrophoblast after the placenta is formed.
- Function: hCG maintain corpus luteum function and promote progesterone secretion. hCG can be tested through urine or blood, which is the basic principle of pregnancy test strips.
The Relationship between hCG Level and Adverse Pregnancy Outcomes
The changing trend of hCG level is more critical than the absolute value, and it has a predictive value in early pregnancy. The following are several adverse pregnancy conditions that are closely related to hCG level:
- Ectopic pregnancy (ectopic pregnancy)
- hCG level rises slowly (usually <66%/48 hours)
- hCG level may be lower than normal intrauterine pregnancy
- No intrauterine gestational sac is seen on ultrasound, and blood hCG ≥1500 IU/L should be alert
Miscarriage or Embryo Arrest
- hCG level decreases or increases slowly
- Single test cannot be diagnosed, but abnormal dynamic monitoring (every 48 hours) indicates embryo maldevelopment
Hydrogenic Mole
- hCG level is abnormally elevated, much higher than normal pregnancy
- Accompanied by severe morning sickness and uterine enlargement
- Some cases develop into malignant trophoblastic tumors
Embryo Development Retardation or Fetal Arrest
- Although hCG level rises, it does not conform to the normal doubling rule
- It can be further judged in combination with progesterone, ultrasound fetal heart rate
Normal hCG Trend in Early Pregnancy
| Weeks of pregnancy (from last menstrual period) |
Serum hCG range (IU/L) |
| 3 weeks |
5 – 50 |
| 4 weeks |
5 – 426 |
| 5 weeks |
18 – 7,340 |
| 6 weeks |
1,080 – 56,500 |
| 7-8 weeks |
7,650 – 229,000 |
| 9-12 weeks |
25,700 – 288,000 |
In a normal intrauterine pregnancy, hCG usually doubles every 48 hours (increase ≥ 66%) in the early stage (first 6 weeks), and the growth rate gradually slows down thereafter.
Clinical Application
- Diagnosis of abnormal pregnancy: hCG levels will rise or fall abnormally in cases of ectopic pregnancy, miscarriage, trophoblastic disease (such as hydatidiform mole, choriocarcinoma), etc.
- Assisted reproductive monitoring: used to determine whether the embryo has successfully implanted.
Notes
- A single hCG test is not sufficient to determine the outcome of pregnancy, and dynamic testing + imaging should be used to make a comprehensive judgment;
- hCG levels vary greatly among individuals and need to be combined with clinical manifestations;
- Certain drugs (such as hCG injections) or diseases (such as trophoblastic tumors, testicular cancer) can also cause elevated hCG.
An Important Factor in Effectively Assessing Pregnancy Status
Human chorionic gonadotropin (hCG) is a hormone produced by the placenta that plays an important role in early pregnancy. hCG levels are closely related to the health of pregnancy, such as ectopic pregnancy, miscarriage, fetal growth retardation, and pregnancy-related complications.
In short, monitoring hCG levels can help doctors assess the health of pregnancy and detect potential problems early so that necessary measures can be taken in time. For pregnant women, regular hCG level testing can provide important health information.
References
- Cole, L., et al. Biological functions of hCG and hCG-related molecules. Reproductive Biology and Endocrinology. 2010, 8: 1-14.
- Nwabuobi, C., et al. hCG: biological functions and clinical applications. International journal of molecular sciences. 2017, 18(10): 2037.
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