The human chorionic gonadotropin (hCG) is an important hormone in the detection and maintenance of pregnancy. Non-pregnant women have very low levels of hCG. However, the hormone exists in high concentration in the bloodstreams of pregnant women. Human chorionic gonadotropin is produced by the embryonic cells after implantation. Once the placenta is formed, it takes over the role of producing hCG. Implantation occurs 6-12 days after ovulation.
The role of hCG in pregnancy
Though witty humans discovered that hCG could be used to test pregnancy and viability of early pregnancy, the primary role of the hormone is maintaining the embryo as discussed below.
Maintaining the corpus luteum
The body produces hCG to maintain the corpus luteum. This a hormone-secreting gland that prepares the uterus for pregnancy. The corpus luteum becomes active few days during ovulation. If fertilization does not occur, the gland becomes inactive. When the ovum is fertilized, the corpus luteum needs to be active so that it can produce hormones that nourish the embryo. hCG is therefore produced after implantation to ensure the corpus luteum remains active.
Maintain the lining of the uterus
Besides maintaining the corpus luteum, hCG maintains the uterine walls. Before the formation of the placenta, the embryo relies on the uterine walls. These walls, therefore, need to undergo several changes after implantation to provide a suitable environment for embryonic development. hCG delivers this environment by maintaining the uterine lining.
You might have heard someone referring to hCG as the “pregnancy hormone.” This is because of its effectiveness in improving fertility. It was discovered that the structure of hCG is almost similar to that of Luteinizing Hormone (LH). The role of LH is to stimulate the release of ova. Due to the structural similarities, hCG can also stimulate ovulation. When LH levels in the body are low, fertility is low because ovulation hardly happens. The injection of hCG can resolve this condition. The hCG injection is particularly helpful to women whose ovaries have mature egg follicles but can’t release eggs. Normally, these ovaries release the egg within two days of receiving hCG injection.
HCG and pregnancy tests
When conducting a pregnancy test, we are essentially trying to detect hCG in blood or urine. The presence of hCG indicates that one is pregnant. hCG is produced after implantation. The hormone can thus be detected in blood two to three days after implantation. In urine, hCG is usually detected three to four days after implantation.
Though hCG can be detected in urine about three days after implantation, if you are using a home pregnancy test, it might take up to two weeks for the hormone to be detected. The amount of hCG in urine two to three days after implantation is not high enough to be detected by the home pregnancy test kit.
When using a home pregnancy test kit, a negative result is less reliable than a positive result. In fact, it is rare to have a false positive result. If you have missed your period, and the home pregnancy test turns out negative, it is advisable to repeat the test after about a week. Home pregnancy tests taken shortly after a missed period may turn out negative since the body has not produced enough hCG.
Changes in hCG levels during pregnancy.
Analysis of the levels of human chorionic gonadotropin during pregnancy is essential in monitoring embryo development. Changes in hCG levels in pregnant women do not follow a specific curve. However, there are ranges beyond which the changes will be considered abnormal.
- Early pregnancy is characterized by a rapid increase in the hCG levels. The following are the different trends of hCG levels during early pregnancy.
- If the hCG level is below 1,200 mIU/ml, the level doubles every two to three days. An increase of 35% within the same time range is still considered normal.
- When the hCG level is between 1,200 and 6,000 mIU/m, it will typically take three to four days to double.
- When the hCG level is above 6,000 mIU/ml, it will typically take more than four days to double.
Usually, when the hCG level exceeds 7200 mIU/ml, a yolk sac should be visible in the uterus. When the concentration exceeds 10,800 mIU/ml, an embryo should be visible.
How is hCG used to determine pregnancy viability
Monitoring the rate of increase in hCG level can be used to determine the viability of a pregnancy. The percentage increase is observed every two days. If a normal rise is recorded within six weeks of pregnancy, it is an indication that the pregnancy is viable. The rate of increase is considered “normal” if the blood hCG level doubles every 48-72 hours. If the rate of increase is slower than usual, it might be an indication of miscarriage or ectopic pregnancy.
Beyond the sixth week of pregnancy, or when the hCG level exceeds 6,000 mIU/ml, the rate of increase in the level of hCG is not related to the development of the fetus. The rate of increase beyond the sixth week is thus not a reliable indicator of the viability of the pregnancy. At this time, the fetal heartbeat is the best indicator of how healthy the pregnancy is.
A variation in the rate of increase in human chorionic gonadotropin concentration is not always an indication that the pregnancy is abnormal. The analysis of the rate of increase should, therefore, not overrule clinical symptoms.
Important points regarding hCG levels and pregnancy
In conclusion, below are the points worth noting regarding the relationship between hCG levels and pregnancy.
- The level of hCG in the blood is measured in milli-international units per milliliter (mIU/ml).
- The level of hCG in urine is lower than that of blood.
- For the first four weeks of pregnancy, the level of blood hCG is expected to double every 48 hours under normal conditions.
- When the blood hCG level is 1,000 – 2,000mIU/ml, a transvaginal ultrasound should detect a gestational sac in the uterus.
- After about ten weeks of pregnancy, the blood hCG level starts falling.
- If the rate of hCG level increase is slower than usual, it might be an indication that the pregnancy is non-viable.
- Beyond six weeks of pregnancy, HCG level monitoring is not a good indicator of the health of the fetus.