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Human chorionic gonadotrophin, or hCG, is a very specific hormone produced during pregnancy. This hormone is what results in a positive pregnancy test. Detecting hCG can be done at home and in a hospital setting using one of several different methods. At-home pregnancy tests are done using urine. Medically performed detection can be done using urine or blood.
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Detecting hCG in Urine and Blood
Numerous brands of home pregnancy tests are available. All rely on the detection of hCG in a woman’s urine. Some brands report being accurate before a woman misses her period while others suggest taking the test a few days or longer after the expected period. The American Pregnancy Association explains that within 12 to 14 days of conception a urine test can detect hCG.
A blood test can identify hCG in early pregnancy within 11 days of conception. Once the blood sample is obtained the health care facility can run one of two specific types of hCG tests. The first is a quantitative hCG measurement, which identifies not only the presence of the hormone but also the quantity that exists. The qualitative hCG measurement simply identifies whether or not hCG exists in the blood, much like a urine test.
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Rise of hCG in Pregnancy
A quantitative hCG test isn’t always necessary to confirm a pregnancy. It is more useful to determine abnormal issues such as an ectopic pregnancy, molar pregnancy and the risk of miscarriage. It is often used with intrauterine fertilization and other fertility treatments to assist a health care professional in determining if the procedure was successful.
Generally, a woman’s hCG level will double every 48 to 72 hours for the first few weeks following implantation, or the attachment of the fertilized egg to the woman’s uterine wall. This will taper off, taking 96 hours or longer for the levels to double in a normal pregnancy. It is possible to have lower than average hCG levels and have a healthy pregnancy. Extremely high levels can indicate one of the more abnormal issues.
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Accuracy of hCG Detection
The health and sustainability of a pregnancy should not be based solely on hCG tests. An early ultrasound performed around the fifth or sixth week of the pregnancy can provide more accurate information according to the American Pregnancy Association. The hCG levels around this time will have reached 1,000 to 2,000 mili-international units per milliliter.
When comparing the reliability of using urine or blood to detect hCG levels in early pregnancy women have to understand that sometimes a urine test will produce a false negative when it is taken too soon. Neither test is more reliable than the other when it is performed too soon. MayoClinic.com explains that most home pregnancy tests, which only use urine, claim to be 99 percent accurate. The clinic argues that research doesn’t support these claims but the timing contributes greatly to their errors. Simply put, a blood test is more sensitive than a urine test but when taken one week after an expected period both tests will produce the same reliable results.
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American Pregnancy Association: Human Chorionic Gonadotropin (hCG): The Pregnancy Hormone http://www.americanpregnancy.org/duringpregnancy/hcglevels.html
MayoClinic.com: Getting Pregnant http://www.mayoclinic.com/health/home-pregnancy-tests/PR00100/NSECTIONGROUP=2
Morrison LJ. General approach to the pregnancy patient. In: Marx J, ed.Rosen’s Emergency Medicine: Concepts and Clinical Practice. 6th ed. St Philadelphia, Pa: Mosby Elsevier; 2006:chap 176.
MedlinePlus: Pregnancy Test http://www.nlm.nih.gov/medlineplus/ency/article/003432.htm