hCG hormone is produced by the placenta as soon as the fertilized ovum is implanted into the uterine wall. The presence of βhCG in plasma shortly after conception, followed by its rapid rise in concentration, makes it an excellent marker for confirmation of pregnancy. Physiologically, hCG appears to maintain the corpus luteum and support the endometrium. Levels increase to a peak concentration during the first trimester, then decrease and plateau during the remainder of the pregnancy. hCG circulates as the intact molecule in the serum of normal women who have an uncomplicated pregnancy.
