The so-called pregnancy hormone, human chorionic gonadotropin or hCG, comes from the embryo. Its job is to help maintain the pregnancy until the placenta fully forms. A "good" level of hCG depends on the exact stage of the pregnancy. Because hCG levels can vary so widely, even in a normal pregnancy, doctors do not check hCG levels over the course of pregnancy unless they suspect a problem.
Role of hCG
Only the cells surrounding an embryo produce measurable amounts of hCG. This hormone has two major roles in pregnancy: it helps the embryo implant in the uterus, and it maintains production of the hormone progesterone from the ovary. The continuous production of progesterone tells the uterus to maintain its rich lining and embedded embryo, rather than shedding it as during a normal menstrual cycle.
Measurement
As soon as 11 days after conception, the blood of a pregnant woman has measurable levels of hCG, according to the American Pregnancy Association. By the 12th to 14th day after conception, measurable levels of hCG appear in the urine. Because only an embryo can produce hCG, its presence in the urine reliably indicates pregnancy when assayed using an over-the-counter pregnancy test. Over-the-counter pregnancy tests are qualitative, meaning they only answer whether or not hCG is present. Quantitative blood tests can tell exactly how much hCG there is.
Levels
The American Pregnancy Association says that as a general rule, hCG levels double about every 48 to 72 hours in a normal pregnancy until they peak at about the 12th week. This means that in later weeks, "normal" hCG levels can vary by an enormous margin. The American Pregnancy Association stresses that it is the change in level, and not the absolute level itself, that indicates how the pregnancy is progressing. The Association presents a range of hCG levels throughout pregnancy as a guideline. In the sixth week of pregnancy, hCG levels range from 1,080 to 56,500 mIU/ml. In the seventh to eighth week, levels increase to about 7,650 to 229,000 mIU/ml. Levels peak at 25,700 to 288,000 mIU/ml in the ninth to 12th week.
Factors to Consider
A single test of hCG does not tell much, because it is more important to know how levels change over time. A few different factors can affect the absolute level of hCG, including the exact date of conception, the number of embryos and whether a woman took fertility drugs containing hCG.
Significance
A "good' hCG level falls within the normal range for the particular stage of pregnancy and rises steadily as the pregnancy progresses. The presence of hCG early in pregnancy means that there is an embryonic sac, but it does not guarantee that there is an embryo inside it. A normal level of hCG followed by a decline in hCG can mean that the embryo never formed, or it formed and died, or that the pregnancy is ectopic. A high hCG level that remains elevated could mean a multiple pregnancy or a molar pregnancy, the implantation of a fast-growing group of cells that will not develop into an embryo.
References
- American Pregnancy Association: hCG
- "Obstetrics: Normal and Problem Pregnancies"; Steven Gabbe, Jennifer Niebyl and Joe Leigh Simpson; 2007
