In early pregnancy, doubling time of beta HCG is-

Ans. is 'b' i.e., 48 hours * Human Chorionic Gonadotropin (hCG): Glycoprotein, with biological activity very similar to luteinizing hormone (LH), both of which act via the plasma membrane LH-hCG receptor. It is secreted by syncytiotrophoblasts.* This hormone is structurally related to three other glycoprotein hormones: LH, FSH, and TSH. The amino acid sequence of the a- subunits of all four glycoproteins is identical.* hCG is detectable in plasma of pregnant women as early as day 22 of menstrual cycle by RRA (radioreceptor assay) or day 25th of menstrual cycle by RIA (radioimmunoassay).* hCG enters maternal blood at the time of blastocyst implantation. Blood levels increase rapidly, doubling every 2 days, with maximal levels being attained at about 8-10 weeks of gestation.* From 10 to 12 weeks the level begins to decline to reach the nadir at 20 weeks. Plasma levels are maintained at this lower level for the rest of pregnancy.* It completely disappears from circulation 2 weeks postpartum.* The best-known biological function of the hCG is the rescue and maintenance of function of the corpus luteum, that is, continued progesterone production.