hCG, which is short for Human Chorionic Gonadotropin, is the hormone that is produced by a woman’s body during pregnancy. hCG is made from cells that make up the placenta. hCG can be detected sometime around 10 to 11 days after conception in the bloodstream, and somewhere around 12 to 14 day in the woman’s urine. This is how pregnancy tests work, by looking for hCG in the woman’s urine. Low doses of hCG, in the less than 5 milli-international units per milliliter (5 mIU/ml) range are present at all times in a woman’s body.
hCG levels will generally continue to double around every two to three days in early pregnancy. Later on in pregnancy, it can take as much as four days for hCG to double. At around the thirteenth week of pregnancy, hCG levels will typically begin to level off, and will continue to do so until the end of the pregnancy.
After a miscarriage, hCG levels do not completely disappear immediately, and it even takes a while for them to get down to the less than 5 mIU/ml range. It can take as much as four to six weeks for hCG levels to return to a non-pregnant range. The time that this takes can depend greatly on whether the miscarriage was spontaneous, or whether there was a D&C involved or many other factors. However, a miscarriage will definitely show a drop off in the levels of hCG, or at least a stagnation of the hCG levels.
There are other things that might cause hCG levels to appear low. Miscalculation of the conception date can certainly make hCG levels appear lower than expected. An ectopic pregnancy, while it will produce hCG, will not have the same rate of increase in hCG levels as a true pregnancy. A blighted ovum may also produce low hCG levels.
High hCG levels can be caused by a variety of factors as well. Again, miscalculating the conception date can factor in here. A molar pregnancy can also cause increased levels of hCG. A pregnancy with twins or multiples can also cause higher levels of hCG.