Fig. 12. Serum hCG secretion in normal pregnancy. Note the rapid early increase (doubling every 48 hours through day 70), peak levels of approximately 200,000 mIU/ml at 8 to 9 weeks, and then declining values to a lower plateau for the remainder of gestation. The wide ranges of variation should be recognized. (Modified from Hon EH: A Manual of Pregnancy Testing, Boston, Little, Brown & Co, 1961)