HCG Levels: What They Mean

October 13, 2008

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HCG Levels: What They Mean

by Marjorie Greenfield, M.D.
reviewed by Marjorie Greenfield, M.D.

Early in pregnancy, a hormone is produced that tells the body conception has occurred. The presence of this hormone, hCG (or human chorionic gonadotropin), sets into place a chain of events, including the continued ovarian production of the hormone progesterone, which helps to sustain the uterine lining and prevents menstruation from starting.

Normally, hCG production increases exponentially, starting a few days after the embryo implants in the wall of the uterus. It can be measured in the blood as early as a few days before your period is due and can often be detected in urine with a regular home pregnancy test by the time you miss a period.

HCG can be tested qualitatively, where the result just says positive or negative (similar to a urine pregnancy test); or quantitatively, where the actual blood concentration of hCG is measured. In the early first trimester, quantitative blood levels of hCG often are used to see if the pregnancy is progressing normally and to estimate the age of the embryo in order to know what to expect to see on ultrasound.

When is quantitative hCG testing necessary?
If your urine pregnancy test is positive and the situation is low risk, there is usually no reason to check a quantitative hCG. However, if there are risk factors for miscarriage or tubal (or ectopic) pregnancy, serum hCG values can sometimes be helpful.

Using hCG levels to assess ultrasound findings
Once the hCG value is known, it can indicate whether the pregnancy is far enough along to be visible in the uterus. For example, an intrauterine pregnancy will be seen on transvaginal sonogram by the time hCG levels reach, on average, 2,000. If the hCG value is more than 2,000 and the pregnancy isn't visible on transvaginal scan, it's likely that the pregnancy is located outside the uterus, in the fallopian tube.

Since these values depend somewhat on the type of hCG test used and the sensitivity of the ultrasound equipment, your ultrasound unit will have its own specific standardized cutoff levels.

Ultrasound also can help to assess the location and viability of the embryo if there are complications or potential problems early in pregnancy. When ultrasound doesn't detect the pregnancy in the uterus, it doesn't always mean that there's an ectopic pregnancy. It could be that the pregnancy is too small to see because the embryo is still too young, or that there has been a miscarriage.

Using hCG testing to assess if the pregnancy is viable

Normal progression of hCG levels. In a healthy pregnancy, blood levels of hCG rise in a predictable pattern, doubling every 48 hours. While some pregnancies follow a slightly slower rate, the lower limit is an increase of 66 percent in two days. Unless there has been a laboratory error, falling hCG levels always mean a nonviable pregnancy. It doesn't matter if the hCG is rising; if it doesn't hit the 66 percent increase by 48 hours, the prospects are grim.

Why do I have to wait 48 hours to get the second test? Two days can seem like forever when you are worried about your pregnancy. But since the amount of hCG rises exponentially, the increase is greatest at the end of the 48-hour time period. In other words, by 24 hours, you may only see a 10 or 20 percent rise, and there's no way to judge if that's normal. It might even not change much for the first 24 hours and still be OK by day two. So you just have to wait the full amount of time.

Is the pregnancy safe if the hCG rises normally? While there is never any guarantee against miscarriage, normally rising hCG values typically indicate that a pregnancy is developing properly.


RELATED INFORMATION

			The Events of Conception
			When an Early Ultrasound Doesn't Show the Embryo
			Getting Pregnant
			Miscarriage
			Moms-to-Be Testing

Created September 14, 2001
Reviewed August 14, 2004

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