Beta-hCG

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

Beta-hCG levels may be used in three ways in the clinical setting of pregnancy:

• 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 should be suspected
• 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 differentiateretained products of conception (RPOC) from gestational trophoblastic disease

It may also be used qualitativelyquantitatively, as a tumour marker, to aid in diagnosing a potentially beta-hCG secreting mass (e.g. choriocarcinoma)

Terminology

"hCG" is an acronyminitialism 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 gonadotrophsgonadotropins, are in this class)

This gonadotropinhCG consists of two moieties:

• an alpha moiety (α) moiety that is similar to FHSFSH, LH, and TSH,

and a

• a beta moiety (β) moiety that is unique to human chorionic gonadotropin

In view of this homology between hCG and other gonadotropins, all commercially-available assay kits test for the beta subunit only. With markedlyThis is to reduce the risk of inadvertently mistaking FH and LSH as part of the hCG fraction. Markedly elevated beta-hCG levels such as which may occur with the gestational trophoblastic disease, thewhilst abundance of the alpha subunit (of hCG) may cause hyperthyroidism ⁷.

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

NB: gonadotropin is the pregnancy.correct spelling; gonadotrophin is an old spelling that should be avoided

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 beta-hCG level a gestational sac should be seen ². These levels are continually revised (values are in mIU/ml/mL):

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

Currently, it is discouraged to treat based on a single beta-hCG level in a hemodynamically stable-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 pregnancy with vaginal bleeding and a beta-hCG level that is not increasing appropriately (or declining) is assumed to be an inevitable miscarriage ⁵, although 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.

Beta-hCG levels decrease rapidly in the first 1-2 weeks after delivery, termination or complete miscarriage and then the rate of decrease slows down beyond 2 weeks. At 6 weeks levels should be zero.

Other

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

On ultrasound, the 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
• RPOCretained products of conception: falling beta-hCG levels

Beta hCG-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