Here is some clear information from the American Pregnancy Assoc.Key things to remember about hCG levels:
*In a bout 85% of normal pregnancies, the hCG level will double every 48 - 72 hours. As you get further along in pregnancy and the hCG level gets higher, the time it takes to double can increase to about every 96 hours.
*Caution must be used in making too much of hCG numbers. A normal pregnancy may have low hCG levels and result in a perfectly healthy baby. The results from an ultrasound after 5 - 6 weeks gestation are much more accurate than using hCG numbers.
*An hCG level of less than 5mIU/ml is considered negative for pregnancy, and anything above 25mIU/ml is considered positive for pregnancy.
*The hCG hormone is measured in milli-international units per milliliter (mIU/ml).
*A transvaginal ultrasound should be able to show at least a gestational sac once the hCG levels have reached between 1,000 - 2,000mIU/ml. Because levels can differentiate so much and conception dating can be wrong, a diagnosis should not be made by ultrasound findings until the hCG level has reached at least 2,000.
*A single hCG reading is not enough information for most diagnoses. When there is a question regarding the health of the pregnancy, multiple testings of hCG done a couple of days apart give a more accurate assessment of the situation.
*The hCG levels should not be used to date a pregnancy since these numbers can vary so widely.
*There are two common types of hCG tests. A qualitative hCG test detects if hCG is present in the blood. A quantitative hCG test (or beta hCG) measures the amount of hCG actually present in the blood.
Guideline to hCG levels during pregnancy:
hCG levels in weeks from LMP (gestational age)* :
3 weeks LMP: 5 - 50 mIU/ml
4 weeks LMP: 5 - 426 mIU/ml
5 weeks LMP: 18 - 7,340 mIU/ml
6 weeks LMP: 1,080 - 56,500 mIU/ml
7 - 8 weeks LMP: 7, 650 - 229,000 mIU/ml
9 - 12 weeks LMP: 25,700 - 288,000 mIU/ml
13 - 16 weeks LMP: 13,300 - 254,000 mIU/ml
17 - 24 weeks LMP: 4,060 - 165,400 mIU/ml
25 - 40 weeks LMP: 3,640 - 117,000 mIU/ml
Non-pregnant females: <5.0 mIU/ml
Postmenopausal females: <9.5 mIU/ml
Info from: http://www.americanpregnancy.org/dur...hcglevels.html