HCG stands for human chorionic gonadotrophin, which is a hormone produced during pregnancy. HCG levels are measured in your urine when taking a home test, and so it is important to understand when HCG is released so that you can take the test at the appropriate time, thereby avoiding false-negative results. HCG levels are good indicators of other features of pregnancy, too, and doctors will often measure these levels in your blood to gauge whether your pregnancy is progressing as it should.
What is HCG?
Human chorionic gonadotropin is a hormone produced in pregnant women by the embryo and the connecting placenta. It is composed of two subunits, alpha and beta, where the alpha subunit is identical to that of the related sex hormones luteinizing hormone and follicle-stimulating hormone. HCG is produced to ensure that pregnancy can be maintained, but it can also be used to stimulate ovulation. A 2004 study published in the "Journal of Reproductive Biology and Endocrinology" showed that women who were given a HCG injection prior to ovulation had a greater success rate conceiving than those who did not receive an injection. In addition, HCG is also administered to women undergoing in vitro fertilization to allow the production of eggs.
What does HCG do?
HCG is released once the embryo has implanted onto the uterus wall, and its function is to stimulate the production of progesterone from the corpus luteum, a temporary structure in the ovary which is responsible for producing progesterone to maintain the uterus wall during pregnancy. Production of HCG occurs particularly in the first trimester. HCG ensures that the uterus lining remains intact for the duration of the pregnancy, allowing the proper development of the fetus. Without the release of HCG, and therefore progesterone from the corpus luteum, the lining would be shed in the same way it is shed during an ordinary period, and there would be a serious risk of miscarriage.
HCG Levels During Pregnancy
As the beta subunit of HCG is produced in pregnancy alone, it has been used as an indicator of conception and is measured in mIU/mL in blood and urine. A 1999 study published in the "New England Journal of Medicine" showed that HCG will be produced immediately after implantation, but most tests can detect HCG in the urine only 8 to 10 days after conception. After this, the HCG levels will double every 48 to 72 hours, although the exact doubling time can vary significantly between individuals. By 9 to 11 weeks, HCG levels peak, and after this the levels will drop off to anywhere between 4,000 and 110,000 mIU/mL for the remaining two trimesters.
Taking a Pregnancy Test
HCG levels in the blood will be below 5 mIU/mL at 7 days after conception, according to the American Pregnancy Association. Most urine tests have a detection level of 25 mIU/mL to indicate pregnancy, and these levels normally are not reliably reached until the first day of a missed period, or at least 14 days after conception. According to the National Women's Health Information Center, 90 percent of women who were pregnant got a positive urine test on the first day of a missed pregnancy. This goes up to 97 percent one week after the first missed period. You can get a false-negative result if you take a pregnancy test too early. Because of the variation in HCG levels between individuals, it is advisable that you wait until the day of your missed period to take the test and that you take more than one test to ensure accurate results.
Abnormal HCG Levels
There are situations where blood tests are taken to measure your HCG levels quantitatively, for example, when particularly high levels of HCG are detected when performing routine blood tests during pregnancy. In such situations, your doctor may want to perform further tests to check whether the doubling time of HCG falls within normal limits. If this is not the case, there is a possibility of ectopic pregnancy or miscarriage, and your doctor should investigate this. If you are concerned about your HCG levels, consult your doctor.
References
- New England Journal of Medicine: Implantation Time of the Conceptus, Urine HCG Detection
- The American Pregnancy Association: HCG Levels During Pregnancy
- "Journal of Reproductive Biology and Endocrinology": Human Chorionic Gonadotrophin Administration
- The National Women's Health Information Centre: Reliability of Pregnancy Tests
