Beta-HCG in early pregnancy

• Whole HCG has both alpha and beta sub chains.
  
• The alpha chain is shared by LH, so that old tests for HCG could give a false positive by detecting the high levels of LH at the time of ovulation.
• The beta chain is unique to HCG.
  
• Output of HCG doubles every 1.5 days in the early weeks and every three days at about eight weeks.
  
• Ectopic pregnancy tends to produce less and the rate of increase is diminished.
  
• By the time normal pregnancy is producing > 6,000 iu./l., an intrauterine pregnancy can be seen on abdominal scan in almost all cases.
  
• (Transvaginal scanning is much more sensitive in detecting intrauterine pregnancy, and will almost always show a pregnancy with HCG levels > 1,000 iu./l.)
  
• Hence levels above these with no scan sighting of an intrauterine pregnancy suggest it is elsewhere.
  
• The same applies to a low rate of increase in HCG levels.
  
• A very low level of HCG after the early weeks is most probably due to a failed pregnancy (assuming the dates are correct) or ectopic pregnancy.
  
• HCG production peaks at about 12 - 14 weeks.
  
• Twin pregnancy and hydatidiform moles produce high levels, which may be the explanation for their association with hyperemesis.

Category: Obstetrics Notes