Beta-hCG

Beta-hCG is a hormone found in the mother's blood serum that can be used to help interpret ultrasound findings.

Beta-hCG levels may be used in three ways:

• qualitatively, for presence/absence of fetal tissue
  • more often determined with a urine test than with a serum test
  • includes or excludes a pregnancy-related differential in a female pelvic ultrasound
• quantitatively, for assessing if a pregnancy is meeting appropriate cutoff values for its age
  • has been used in the first trimester to help determine if an ectopic pregnancy is suspect
• quantitatively, for trending the growth rate of fetal tissue
  • has been used in the first trimester to help determine if a pregnancy is failing
  • has been used to differentiate retained products of conception (RPOC) from gestational trophoblastic disease

It may also be used qualitatively to aid in a diagnosing a potentially Beta-hCG secreting mass (e.g. choriocarcinoma)

Terminology

"hCG" is short for "human chorionic gonadotropin"

• chorionic: produced from the syncytiotrophoblasts of the chorion, which are developing into the fetal placenta
• gonadotropin: a substance that regulates gonadal activity (FSH and LH, anterior pituitary gonadotrophs, are in this class)

This gonadotropin consists of two moieties: an alpha moiety that is similar to FHS, LH, and TSH, and a beta moiety that is unique to human chorionic gonadotropin. With markedly elevated beta-hCG levels (such as may occur with gestational trophoblastic disease), the abundance of the alpha subunit may cause hyperthyroidism ⁷.

The role of the hormone is to maintain the corpus luteum, thereby maintaining a favorable intrauterine environment for the pregnancy.

Differential diagnosis

Quantitative for gestational sac visualisation

The use of beta-hCG values to guide interpretation of first trimester ultrasound findings has a long history. "Discriminatory levels" were first devised to indicate at what hCG level a gestational sac should be seen ². These levels are continually revised (values are in miU/ml):

• >0
  • ​fetal chorionic/placental tissue is present somewhere
• >1000-2000
  • ​older cut off for visualisation of an intrauterine gestational sac
• >2000
  • ​nonvisualisation of the intrauterine gestational sac is suspicious for an ectopic pregnancy, but does not exclude a normal IUP ³

Currently, it is discouraged to treat based on a single hCG level in a hemodynamically stable woman with a pregnancy of uncertain location ³.

Quantitative for trending

Beta-hCG values can also be used to determine if a pregnancy is progressing appropriately (until about ~10 weeks gestational age)

• <8 weeks of pregnancy (gestational age)
  • beta-hCG level is assumed to double every ~48 hours ⁴
• 8-10 weeks of pregnancy
  • beta-hCG level is assumed to double approximately every ~5 days ⁴

A pregnant patient with vaginal bleeding and an hCG level that is not increasing appropriately (or declining) is assumed to be an inevitable miscarriage ⁵, although this solidity of this idea after 8 weeks and above a level of 5000 miU/ml has been questioned ⁶.

Trending beta hCG levels can help differentiate a cervical ectopic pregnancy from an inevitable miscarriage.

Other

Gestational trophoblastic disease (e.g. complete mole) is associated with very elevated hCG levels.

On ultrasound, gestational trophoblastic disease may appear radiologically similar to retained products of conception (RPOC), but the two may be differentiated with beta-hCG

• gestational trophoblastic disease: markedly elevated beta-hCG levels
• RPOC: falling beta-hCG levels

Beta hCG levels may also be raised by some ovarian neoplasms (e.g. ovarian embryonal carcinoma, ovarian dysgerminoma), as well as in testicular germ cell tumours ⁸. 

See also

• tumour markers