HCG stands for human chorionic gonadotropin. It is one of the pregnancy hormones that is responsible for the presence of a positive pregnancy test. It is made by the embryo as it implants inside the uterine wall and increases up until about the tenth week of gestation.
The hCG level is the level in the urine or blood of human chorionic gonadotropin. This is a protein-based hormone the placenta of the embryo and growing fetus makes. HCG levels in early pregnancy begin to rise upon implantation and increase throughout the first trimester. There are two kinds of hCG pregnancy test types. The first is the qualitative hCG level. This is a positive or negative test of the urine that detects the presence of hCG at between 25 and 50 IU/ml. The second is the quantitative hCG test. It is a test of the blood that detects the exact amount of hCG in the blood. It is useful in very early pregnancy and can help detect the presence of a possible miscarriage.
No one knows the exact function of human chorionic gonadotropin. It is a hormone produced by the placenta and by some hCG-secreting cancers. It isn’t necessary throughout the entire pregnancy as the value goes way down by the end of the pregnancy. How does hCG work? No one knows that either. It seems to be supportive of the pregnancy in the early stages.
Normal hCG levels vary widely and are different from day to day during early pregnancy. In the beginning, levels go from 0 to about 50 IU/ml, at which time the pregnancy test becomes positive. It doubles every 48-72 hours or so in early pregnancy, reaching levels that can be in excess of 10,000 IU/ml. Some women have low hCG levels in the early part of pregnancy, which can indicate a problem with the pregnancy.
Hormone levels can be detected in a urine or blood test. Usually, a first morning specimen of urine is taken and the urine has an applicator dipped into it. It is absorbed by the test applicator and, if you are pregnant, a positive sign or the word “positive” comes up in the reading window. In a blood test, the blood is drawn and a lab machine identifies the exact amount of hCG in the blood. In cases where a suspected miscarriage is present, an hCG level chart is plotted, which shows the exponential increase in hCG levels in the early part of pregnancy.
Low hCG levels are detected:
In these situations, a quantitative hCG level is taken a couple of days apart to see if there is the normal doubling of the hCG levels during that time. HCG levels after miscarriage can also below and drop to normal a few weeks after the miscarriage is over with. So the reasons for low hCG levels are usually ominous to the pregnancy but can simply mean that the dates are off and the pregnancy is earlier than expected.
Normally doctors don’t measure the hCG levels by week. As mentioned, the level tends to go up exponentially in early pregnancy so that the average hCG levels by week increase to about 10,000 IU/ml by about week six-ten and then begin t drop off after that. Miscarriage hCG levels are different. They do not go up exponentially and may remain at the same level or may decrease, indicating that the miscarriage has occurred. Early pregnancy hCG levels begin to show up at the point in time when the embryo implants in the uterus. If the pregnancy is normal, the hCG increase is quite rapid and this is possibly why women have morning sickness early in the pregnancy.
Twin hCG levels are usually much higher than with singleton pregnancies because there are two placentas secreting hCG instead of just one. A twin hCG level chart will show a much greater rise in hCG levels over time and the hCG levels on a quantitative basis will be much higher. This is why many women with twins have a greater degree of nausea and vomiting in pregnancy when compared to women who have just one fetus in their uterus. If there are triplets or more, the hCG levels are extremely high and the incidence of morning sickness is even higher than with twins.
The molar pregnancy hCG levels are very high. A molar pregnancy is actually a tumor inside the uterus that has grown instead of a normal fetus. The uterus is filled with an amorphous substance that secretes abnormal hCG levels elevated much beyond those seen in a regular pregnancy. While a molar pregnancy is not an emergency, once it has been established that a molar pregnancy exists, it must be evacuated from the uterus so that it doesn’t grow out of control. Molar pregnancies never lead to a normal fetus and are an aberrancy of the pregnancy process.
HCG levels will not increase until the embryo has been implanted. Shortly after that, a quantitative blood test can be drawn, which will sensitively pick up the fact that the hCG level is higher than a zero level. This is often done when the woman has undergone in vitro fertilization and the doctor needs to know if any of the inserted embryos have been implanted in the uterus. If a blood test is not indicated or if the woman simply wants to know if she is pregnant, a urine pregnancy test can be done. This is a qualitative test that shows positive when the embryo has been implanted for a couple of days. Many home pregnancy tests claim to be able to detect a positive pregnancy test about 5 to 6 days before a missed period but this is not absolute.
They are only 99 percent accurate on the day you actually miss your period. It means you should repeat the pregnancy test if you have done it early in the pregnancy and before you have missed your period until the pregnancy test finally becomes positive.
In an ectopic pregnancy, which is a pregnancy usually found in the fallopian tubes instead of the uterus, the hCG levels are generally normal. As the pregnancy grows and gets crowded out by the fallopian tube, the hCG levels will not rise as rapidly and will eventually begin to fall as the products of conception die. After the ectopic pregnancy has been treated surgically or treated with methotrexate, the source of the hCG is gone and the levels quickly reduce to normal. Most people do not need to check a repeat hCG level after an ectopic pregnancy unless there is some question that the treatment has failed to work.
Sometimes the hCG level is not elevated because of a pregnancy. Instead, the individual has instead developed a tumor that secretes hCG as part of a tumor marker. Cancers of the ovaries, testes, lungs, and other areas of the body can secrete extremely high levels of hCG. The symptoms can be similar to having nausea and vomiting of pregnancy. Doctors use the hCG levels in these situations not to follow a pregnancy but to see if the tumor is getting better after surgery, chemotherapy, or radiation. HCG-secreting tumors are not common but, when they are detected, the level of hCG is a good way to see if the tumor has resolved itself or if it has metastasized.
Quantitative hCG testing, as mentioned, needs to be done in a doctor’s office. The doctor takes a sampling of the blood. You do not have to be fasting for this type of blood test. The blood is then spun to get the serum part of the blood. It is the serum that is where the human chorionic gonadotropin is found. The serum is removed from the red blood cells to be sampled for the level of hCG in the liquid part of the blood. A machine is used that detects the exact amount of hCG in the serum.
This is a very sensitive test and can detect levels of hCG at any level greater than 5 IU/ml. It is a test often used when there is a suspected ectopic pregnancy or miscarriage because it shows the absolute value of the hCG. Normally, this number should double every 48 to 72 hours and, if it doesn’t do that, it could mean that there is something wrong with the pregnancy. The doctor will take more than one quantitative hCG test in order to see if the doubling happens as predicted. Quantitative hCG levels are also done when the woman has undergone an in vitro fertilization procedure.
The doctor wants to know if the embryo or embryos inserted in the uterus have implanted and the quantitative hCG test will show if this has occurred. It won’t usually be able to detect the number of embryos that have implanted because the hCG levels in any pregnancy fluctuate widely. It is not known why some women have lower hCG levels and why some women’s hCG levels are markedly high.
For reasons that are unclear, the hCG level peaks at around 8 weeks’ gestation and begins to drop after that. This means that the hCG level can technically be below detectable levels when a woman is nearly about to give birth. This is not a worrisome sign and fortunately, a woman rarely has to check her hCG level in late pregnancy because she has many other signs of pregnancy to show that she is pregnant, such as fetal movement and a large uterine size. If an hCG level is obtained and is low or zero, it doesn’t mean she is not pregnant but just means the levels are now undetectable.
When a woman has a triplet pregnancy, she has three separate fetuses and usually has three separate placentas if this is a fraternal triplet situation. Each placenta will give off its own human chorionic gonadotropin so that levels of hCG rise much beyond that seen in a singleton or even a twin pregnancy. The levels of hCG can be in excess of 30,000 IU/ml. This can cause extreme amounts of nausea and vomiting during the pregnancy that can last longer than the first trimester and can occur in the second trimester as well.
In a miscarriage, the levels of hCG are usually abnormal. You may have a positive pregnancy test at the time of the missed menstrual period but the line may be very faint and will not darken with time. A quantitative hCG level will be normal in the early stages of the pregnancy. Unfortunately, the levels of hCG do not usually double in 48 to 72 hours as happens in a normal pregnancy. Instead, they remain steady or begin to fall off.
When the bleeding starts, the products of conception will separate from the inner lining of the uterus and no more hCG will be secreted into the mother’s bloodstream. The levels of human chorionic gonadotropin will begin to fall off and will return to normal within a few weeks of a completed miscarriage. If the products of conception are retained in the uterus, the levels of hCG may remain up but will not approach the levels of a normal pregnancy.
There will usually not be enough hCG to cause any type of nausea and vomiting and, after a dilatation and curettage, the hCG levels will return to pre-pregnancy levels, which is less than 5 IU/ml or even to a zero level.