Human chorionic gonadotropin, or HGC, is a hormone produced during early pregnancy. Because levels of HCG increase significantly from normal levels during pregnancy, pregnancy tests commonly use this hormone as an indicator of whether a woman has conceived. Doctors also measure HCG during early pregnancy to ascertain whether the embryo is growing normally.
Hormone Production
The new embryo begins producing HGC shortly after fertilization. The function of HGC is to stimulate the mother's body to produce progesterone, a hormone necessary for the continuation of the pregnancy. As the pregnancy progresses, more and more HGC is produced until sometime between 8 to 11 weeks after conception. At this point, production slows from doubling every 48 to 72 hours to doubling every 96 hours. The reason for this slowdown is that high levels of HGC are no longer needed once the placenta begins producing progesterone and estrogen at around the 60th day after the last menstrual period.
Testing
Pregnancy tests measure HCG in the mother's urine or blood to determine whether a fertilized egg is present. A blood test can detect HCG about 11 days after conception and a urine test after 12 to 14 days. A measurement of 25 milli-international units per milliliter, or mIU/ml, indicates that the woman is pregnant. Levels under 5 mIU/ml are considered a definitive negative test. Once levels reach between 1,000 to 2,000 mIU/ml, a doctor should be able to verify pregnancy using a tansvaginal ultrasound.
Concerns
Because all women and all pregnancies are different, a low or high HGC level does not necessarily indicate a problem with the pregnancy. In most cases, if the level of HCG is doubling on schedule, the actual number does not matter as much. However, a woman with a low HGC level may require additional tests, such as an ultrasound, to rule out a miscarriage or ectopic pregnancy. Women with unusually high HCG levels may be carrying two or more babies. Unusual or unexpected HCG levels could also indicate that the dating for the pregnancy is incorrect.
Other Uses
HCG is sometimes used in fertility treatment to induce ovulation in women and to increase sperm count in men. When used in women, it may show up on pregnancy tests, making it difficult to tell whether the woman is actually pregnant or not. HCG given for fertility treatment generally clears out of a woman's system by 14 days after treatment. Young boys with pituitary disorder may also be given shots of HCG as treatment.
References
- American Pregnancy Association: Human Chorionic Gonadotropin
- Advanced Fertility Center of Chicago: Early Pregnancy HGC Levels and Ultrasound Pictures
- Drugs.com: Human Chorionic Gonadotropin
- "Human Physiology: From Cells to Systems"; Lauralee Sherwood; 2008
