hCG Levels in Early Pregnancy
The abbreviation hCG is short for “human chorionic gonadotropin” hormone. This is the hormone that pregnancy tests look for, typically a week or two after conception, when your body begins producing various hormones to ensure that your developing baby receives all the nutrients and oxygen it needs. The hCG hormone is made by the cells that form the placenta. The detection of hCG in urine via a home pregnancy test may be the first indication that you are pregnant. Since hCG is only made by placental cells, it is not normally found in the body, thus the detection of even a very small amount of hCG in the body indicates that placental cells are present.
There are two types of hCG tests: qualitative hCG tests, which detect the presence of the hormone in urine or blood, and quantitative hCG tests, which measure the amount of hCG present in the blood. Quantitative hCG tests are also known as beta hCG tests (doctors have nicknamed the test a “quant beta”). The hCG hormone can typically be detected in the urine eight to fourteen days after conception, and in the blood as early as six days after implantation—before the first missed menstrual period. Measuring hCG levels is the best way for healthcare professionals to detect early abnormalities after the pregnancy has been established. In 85 percent of pregnancies, hCG levels double every 72 hours before peaking between the eighth and eleventh weeks of pregnancy. After peaking, the levels begin to decline between the twelfth and sixteenth weeks of pregnancy, and then level off until after childbirth.
What do hCG Levels Mean?
The hCG hormone is produced throughout your pregnancy. Initially hCG maintains the corpus luteum, which is responsible for progesterone production during the early stages of pregnancy. Progesterone’s major job is to maintain the thickness of the uterine lining. A thick lining increases the chances of a healthy pregnancy. If there is no hCG present in your body, the lining will begin to shed and you will begin your period shortly after. Basically, in a normal menstrual cycle, the corpus luteum is created right after ovulation, and it has a lifespan of 12–13 days (producing progesterone). When pregnancy does not occur, the corpus luteum disappears, progesterone production stops, and the menstrual period occurs after a day or two.
The most important thing to remember when examining hCG levels is that every pregnancy is different, and every woman is different. What is normal for one woman is not necessarily normal for another woman. Some women have low hCG levels throughout their pregnancies and have healthy babies. Some have extremely high hCG levels in early pregnancy and can still go on to miscarry.
The hCG hormone is measured in milli-international units per milliliter, or mIU/ml. Typically, when you are not pregnant, your levels are less than 5 mIU/ml. When you are pregnant, your hCG levels will be 25 mIU/ml or higher. If levels are higher than expected based on how far along you are, it may indicate twins or multiple fetuses, a molar pregnancy, or a miscalculation of the pregnancy date. Unexpectedly low hCG levels may also indicate a miscalculation of the pregnancy date, or possibly a miscarriage, an ectopic pregnancy, or a blighted ovum (another type of miscarriage). Often one measurement is not enough. Second or third measurements, especially taken days apart, can yield more accurate results.
Fertility drugs that contain hCG may affect your hCG levels. You and your healthcare provider should discuss this topic if you are currently taking fertility drugs. Other medications such as antibiotics or oral contraceptives do not affect your hCG levels.
If you decide to use a home pregnancy test before seeing your doctor, be aware that all home pregnancy tests detect only the presence of hCG in urine, and the level of hCG each test can detect varies. While urine tests are convenient and relatively inexpensive, they are not as accurate as quantitative blood tests, and can produce false positive results.
hCG and Birth Defects
Depending on your fertility history, age, past pregnancies, and other factors, your doctor may want to track the rise in hCG over a few days or weeks. This means going in for a second, third, or fourth blood test. In a healthy pregnancy, the results should double every 48 to 72 hours. An hCG level that does not rise as expected may indicate a problem with the pregnancy, such as a miscarriage or an ectopic pregnancy.
Pregnancy testing is not the only reason to test hCG levels. They are also used to detect fetal abnormalities that may result in birth defects. During a prenatal visit, your doctor may want to give you a Quadruple Screen Blood test. This test measures the alpha fetoprotein levels, as well as the levels of hCG, estriol (a form of estrogen) and inhibin-A to help evaluate the risk that your baby might have Down syndrome or a spinal or brain abnormality. hCG can also help determine whether a miscarriage has occurred or is going to occur.
hCG Levels and Gender
In a human reproduction study conducted by a team of Israeli researchers led by Dr. Yuval Yaron, 1,325 pregnant women were tested at 10–13 weeks to compare hCG levels between women carrying female fetuses and women carrying male fetuses. The findings were conclusive: women who had a female fetus had significantly higher hCG levels than women carrying males.
The authors noted that the reason for the gender-related difference in maternal serum hCG has remained elusive since the phenomenon was first described in 1965. Based on these studies, some have speculated that it may be possible for woman carrying a male fetus to have a delayed positive urine pregnancy test result because of the lower level of hCG. However, Dr. Yaron and his colleagues concluded that while the gender-related difference in maternal hCG levels is statistically significant, it has little value in predicting fetal sex because of the small proportion of pregnant women with serum HCG concentrations that are high or low enough to allow a prediction with high probability.
In other words, there is no way to definitively know the gender of the baby you’re carrying without undergoing one of the following:
- Amniocentesis or chorionic villus sampling, both of which are invasive and costly.
- A blood test to detect Y chromosome-specific DNA (the presence of Y chromosome DNA confirms a male fetus). This noninvasive test can be done at 10 to 12 weeks’ gestation and may or may not be covered by insurance but may be less costly than invasive methods.
- Ultrasound evaluation: evidence of fetal sexual organs can sometimes be detected as early as the 12th week of pregnancy, although more often not until 16 weeks.
Although it might be fun to speculate about the gender of your baby if your doctor tells you your hCG level after quantitative blood testing early in pregnancy, it would wise to wait until after definitive test results before picking out baby clothes and colors for the nursery.
Additional facts about hCG levels:
- Later in pregnancy, hCG levels mean little to how well the pregnancy is doing
- hCG levels should not be used to date pregnancies, since the numbers vary so widely from woman to woman
- Single hCG tests are typically not enough for an accurate diagnosis
- A transvaginal ultrasound should be able to show a gestational sac if the hCG levels have reached 1,000 to 2,000 mIU/ml. Ultrasound findings lower than 2,000 mIU/ml should not be used to determine the date of conception because levels can vary greatly. For example, hCG levels are much higher for twins, so a very high level of hCG without the presence of a gestational sac might also mean a twin pregnancy.
- Urine hCG levels are typically lower than blood levels