Human chorionic gonadotropin, also called hCG, is produced during pregnancy when the embryo implants into the uterine wall. Human chorionic gonadotropin is the hormone that pregnancy tests use to determine pregnancy. Human chorionic gonadotropin levels rise during the first several months of pregnancy if the embryo develops normally. If the embryo doesn't develop, hCG levels won't rise appropriately. There is nothing you can do to increase hCG levels; they're produced by placental tissue and normally increase only if the embryo grows normally.
Purpose
The production of hCG signals the corpus luteum, the leftover part of the follicle that contained the egg, to keep producing progesterone. Progesterone prepares the uterine lining for implantation by thickening it with extra nutrients and blood vessels. If no embryo implants, the corpus luteum degenerates, the uterine lining breaks down and your menstrual period begins. If the corpus luteum detects the presence of hCG, it continues to produce progesterone and the lining continues to support the embryo's growth.
Normal Levels
The exact levels of hCG aren't as important as their continual rise; the hCG level should double every 48 to 72 hours. At the time of the first missed period, hCG levels average around 48 milli-international units per milliliter, or mIU/ml, according to the Advanced Fertility Center of Chicago, but lower or higher numbers are not significant, as long as they double every 2 to 3 days. Levels increase until week 8 to 10 of pregnancy and then level off, since the placenta completely takes over progesterone production at this time.
Significance
Normally rising hCG levels indicate a normally developing embryo; in 85 percent of normal pregnancies, the hCG level doubles by 72 hours in early pregnancy, Advanced Fertility Center of Chicago explains. After a few weeks, doubling slows, occurring only every 96 hours, the American Pregnancy Association explains. Numbers that don't rise indicate a problem with the pregnancy, usually a chromosomally abnormal embryo. No medications, treatments, bed rest or other methods will increase falling hCG levels if an abnormal embryo has implanted. In most cases, a slow rising or falling hCG signals that miscarriage will occur or that the pregnancy has implanted in the tube rather than in the uterus.
Variations
While the time between ovulation and the next menstrual period is quite consistent, between 12 and 14 days, the time from the start of the last period until ovulation can vary considerably. Stress, illness, strenuous exercise and other factors can cause ovulation to occur later than normal in a cycle. If you ovulate on day 20 rather than day 14, taking a pregnancy test on day 28 may yield very low or negative hCG levels, because the embryo either hasn't implanted yet or has just implanted. This can cause undue concern about the viability of the pregnancy but doesn't indicate a problem, as long as hCG numbers rise appropriately.
Considerations
While appropriately rising hCG levels are important, presence of a growing embryo with a strong heartbeat on ultrasound after 5 to 6 weeks is a better predictor of a normal pregnancy, Advanced Fertility Center of Chicago stresses. Once the hCG level reaches 1,800 to 2,000 mIU/ml, a gestational sac should be seen in the uterus. Failure to see a uterine sac indicates a possible tubal pregnancy, according to the American Pregnancy Association.
