The HCG pregnancy test is a common medical testing method and has many specific applications in the fields of obstetrics and gynecology, etc.

The following is a detailed introduction:

Urine Test
After a woman becomes pregnant, the trophoblast cells begin to secrete HCG after the fertilized egg implants. Generally, around 10 days after pregnancy, HCG can be detected in the urine. The common early pregnancy test strips on the market are based on this principle. Women can conduct the test at home by themselves. The operation is simple, and it can preliminarily determine whether they are pregnant.
Blood Test
The blood test for HCG is more sensitive and accurate. Usually, an increase in HCG in the blood can be detected about 7 days after conception. By quantitatively detecting the specific value of HCG in the blood, doctors can more precisely determine the pregnancy situation. For example, the doubling situation of β-HCG, etc., helps to evaluate the early development status of the embryo.

In a normal intrauterine pregnancy, the HCG level will rise regularly with the increase of the gestational week, generally doubling every about 48 hours. In the case of ectopic pregnancy (pregnancy outside the uterus), since the embryo implants in a location outside the uterus, such as the fallopian tube, the development of trophoblast cells is limited, and the HCG level rises slowly and fails to reach the doubling rate of a normal intrauterine pregnancy.
Combined with ultrasound examination, if no gestational sac is found in the uterine cavity and the blood HCG level does not conform to the growth pattern of a normal pregnancy, doctors will highly suspect ectopic pregnancy to take timely measures and avoid serious consequences such as fallopian tube rupture.

Threatened Miscarriage
For pregnant women with symptoms of threatened miscarriage such as vaginal bleeding and abdominal pain, dynamically monitoring the HCG level can help determine the prognosis of the embryo. If the HCG level continues to rise and the increase range is normal, it indicates that the embryo may still be developing normally. If the HCG level does not rise but decreases, or rises slowly, it suggests that the embryo may have poor development and is at risk of miscarriage.
Hydatidiform Mole
The HCG level in patients with hydatidiform mole is usually abnormally high, much higher than that in the same period of a normal pregnancy. After the curettage of a hydatidiform mole, HCG also needs to be monitored regularly. If the HCG level does not decrease smoothly or rises again after a decrease, it may indicate the residue of hydatidiform mole tissue or malignant(malignant transformation), and further examination and treatment are required.
Choriocarcinoma
This is a highly malignant trophoblastic tumor, which can also lead to a significant increase in the HCG level. By monitoring the changes in HCG, combined with clinical symptoms and other examinations, it can be used for the diagnosis, evaluation of treatment effects, and recurrence monitoring of choriocarcinoma.

In assisted reproductive technologies such as in vitro fertilization (IVF), the HCG pregnancy test plays an important role. After embryo transfer, by detecting the HCG level in the blood, it can be determined whether the embryo has successfully implanted.
Doctors will also adjust treatment plans such as luteal support according to the changes in HCG to increase the success rate of pregnancy and ensure the normal development of the embryo.

Differentiating the Causes of Amenorrhea
For women with amenorrhea, detecting HCG can first rule out amenorrhea caused by pregnancy. If the HCG test is negative, other causes of amenorrhea, such as endocrine disorders and intrauterine adhesions, can be further considered, so as to conduct targeted examinations and treatments.
Monitoring Fetal Development
At different stages of pregnancy, continuously monitoring the HCG level combined with other examination indicators, such as measuring the size of the fetus and the condition of the amniotic fluid through ultrasound examination, can comprehensively evaluate the development status of the fetus and timely detect potential problems such as fetal growth retardation.