|According to the American Pregnancy Association, the hCG level doubles every 48 - 72 hours in around 85% of normal pregnancies during the first trimester.|
Human chorionic gonadotropin (hCG) is a hormone which is produced by the placenta, and helps in the detection of pregnancy. The production of hCG starts after the implantation of the fertilized egg to the uterine wall. It can be detected in blood about 11 days after conception, and in the urine 12 - 14 days after conception. Therefore, tests are conducted to check for the presence of hCG in the blood or urine to confirm pregnancy. hCG is also responsible for ensuring that progesterone is continuously released by the corpus luteum. Progesterone plays a vital role in maintaining the uterine lining, which in turn, is essential for supporting the pregnancy. The levels of hCG rise considerably during early pregnancy, with the hormone secreted in larger amounts by the placental tissues. hCG levels peak between the eighth and eleventh week of pregnancy, and decline thereafter.
hCG Levels and the Detection of Pregnancy
hCG can be detected in the blood, as well as urine. Usually, six to twelve days after ovulation, the rise in hCG levels is substantial enough to give a positive result for the test. Around 5% of pregnant women have detectable levels of hCG eight days after conception, and almost all women have detectable levels of hCG after eleven days. There are two types of tests, when it comes to measuring hCG levels in the blood. A qualitative hCG blood test can only tell you if you are pregnant or not, whereas the quantitative test measures the total amount of hCG in the blood. After the implantation, for the next several weeks, the hCG levels increase exponentially, doubling every 48 to 72 hours. This is referred to as hCG doubling time.
As the pregnancy progresses, the doubling time increases to around 96 hours. It must be noted that the way hCG levels rise may vary from woman to woman, which is why this test must not be used to date pregnancies. Gynecologists don't solely rely on a single hCG reading, when it comes to doubling time. Readings that are taken a few days apart will certainly give a clearer picture. Besides monitoring hCG levels regularly, gynecologists stress on studying the ultrasound findings for an accurate assessment.
Pregnancy is confirmed when the hCG levels are above 25 mIU/ml. Women who are not pregnant have a hCG reading that is below 5 mIU/ml. The following table provides the hCG levels in the weeks following the last menstrual period (LMP).
|hCG Levels in Pregnant Women|
|Weeks after LMP||HCG levels for single baby (in mIU/ml)|
|3 weeks||5 to 50|
|4 weeks||5 to 426|
|5 weeks||18 to 7,340|
|6 weeks||1,080 to 56,500|
|7 to 8 weeks||7,650 to 229,000|
|9 to 12 weeks||25,700 to 288,000|
|13 to 16 weeks||13,300 to 254,000|
|17 to 24 weeks||4,060 to 165,400|
|25 weeks to childbirth||3640 to 117,000|
Pregnancy can be confirmed if hCG levels increase, doubling after every two or three days. When the hCG levels reach 2000 mIU/ml, some type of development can be detected in the transvaginal ultrasound. In case of a transabdominal ultrasound, development is likely to be observed when the hCG level goes beyond 3600 mIU/ml. After this, the levels will slowly begin to decline between the twelfth and sixteenth week. After the sixteenth week, hCG levels tend to remain at a low level till the birth of the baby. The reason why the hCG levels in pregnancy eventually decrease is that once the placenta grows to a substantial size, it takes over the function of progesterone, which is to ensure that the fetus grows normally, and there is no interruption in the lining and thickness of the uterus.
Though the hCG test is essential for the detection of pregnancy, and it also throws light on whether the pregnancy is normal during the first trimester, an ultrasound is a far more reliable tool after 5 - 6 weeks of pregnancy. It must be noted that a slow-rising doubling time in the early weeks, may or may not be a sign of pregnancy-related complications. However, under such circumstances, medical experts would conduct diagnostic tests regularly so as to assess if the pregnancy is progressing normally. In some cases, consistently low levels of hCG in the early weeks could indicate the risk of ectopic pregnancy (pregnancy wherein the fertilized egg implants itself in a place other than the uterus) or a miscarriage. Similarly, consistently high levels of hCG could be indicative of multiple pregnancy or molar pregnancy.
Disclaimer: The information provided in this article is solely for educating the reader. It is not intended to be a substitute for the advice of a medical expert.