Beta-hCG

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Beta-hCG (bHCG or 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 cut-off 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

    • Outside the pregnancy setting, it may also be used quantitatively as a tumor marker, to aid in diagnosing a potentially beta-hCG secreting mass (e.g. choriocarcinoma).

    Terminology

    "hCG" is an initialism for "human chorionic gonadotropin". Chorionic refers to the production of hCG from the syncytiotrophoblasts of the chorion which are developing into the fetal placenta. Gonadotropin refers to a substance that regulates gonadal activity (for instance FSH and L, the two anterior pituitary gonadotropins, are in this class).

    hCG consists of two moieties:

    • an alpha (α) moiety that is similar to FSH, LH, and TSH, and a
    • a beta (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. This is to reduce the risk of inadvertently mistaking FH and LSH as part of the hCG fraction.

    Markedly elevated beta-hCG levels may occur with gestational trophoblastic disease, whilst an abundance of the alpha subunit (of hCG) may cause hyperthyroidism .

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

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

    Differential diagnosis

    Quantitative for gestational sac visualization

    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 . These levels are continually revised (values are in mIU/mL):

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

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

    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
    • 8-10 weeks of pregnancy
      • beta-hCG level is assumed to double approximately every ~5 days

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

    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
    • retained products of conception: 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 tumors .

    See also

    • tumor markers

    • automatic online beta-hCG doubling time calculator from www.perinatology.com