A blood pregnancy test can detect the presence of the hormone human chorionic gonadotropin (hCG) in a blood sample. High levels of hCG indicate a pregnancy.
Most pregnant women find out that they are pregnant by taking a home urine pregnancy test. However, sometimes the doctor orders a blood pregnancy test. hCG rises rapidly in the first ten weeks after a fertilized egg attaches itself to the inner wall of the uterus. This increase can be detected both by testing the urine and by testing the blood.
While urine pregnancy tests are generally reliable, a blood test done by a laboratory is even more reliable. The blood test is able to detect earlier (hGC hormone appears in the blood well before passing into the urine) and with greater precision the presence and possibly the quantity in the circulation of beta HCG.
Blood pregnancy tests are particularly useful,
- to women who urgently need to know their condition immediately;
- to evaluate the possible presence of an ectopic pregnancy ;
- or for monitoring following spontaneous abortions .
The results of laboratory tests are usually known within twenty-four hours.
In addition to confirming pregnancy, blood pregnancy tests also allow you to estimate the presumed date of delivery more precisely, starting from the detection of the concentration of hormones.
No preparation is needed for blood pregnancy tests.
Ranges of hCG in pregnant women
The expected hCG values depend on the week of pregnancy you are in:
- 3 weeks: 5 – 72 mIU/ml
- 4 weeks: 10 -708 mIU/mL
- 5 weeks: 217 – 8,245 mIU/ml
- 6 weeks: 152 – 32,177 mIU/ml
- 7 weeks: 4,059 – 153,767 mIU/ml
- 8 weeks: 31,366 – 149,094 mIU/ml
- 9 weeks: 59,109 – 135,901 mIU/ml
- 10 weeks: 44,186 – 170,409 mIU/ml
- 12 weeks: 27.107 – 201.165 mIU/ml
- 14 weeks: 24.302 – 93.646 mIU/ml
- 15 weeks: 12,540 – 69,747 mIU/ml
- 16 weeks: 8,904 – 55,332 mIU/mL
- 17 weeks: 8,240 – 51,793 mIU/mL
- 18 weeks: 9,649 – 55,271 mIU/ml
Blood hCG pregnancy test, how it is done
After a healthcare professional inserts the needle into your arm, they take a blood sample and put it into a test tube or vial. You may feel a small prick as the needle goes in or out. This process typically takes less than five minutes.
Blood pregnancy test, when
Blood pregnancy tests can detect hCG in the blood six to eight days after ovulation.
The detection of a higher than normal beta-hCG
Detection of higher than normal levels of human chorionic gonadotropin (hCG) may indicate:
- a twin or multiple pregnancy,
- a molar pregnancy (abnormal pregnancy that will not carry to term).
Katherine Johnson, M.D., is a board-certified obstetrician-gynecologist with clinical expertise in general obstetrics and gynecology, family planning, women’s health, and gynecology.
She is affiliated with the Obstetrics and Gynecology division at an undisclosed healthcare institution and the online platform, Maternicity.com.