This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Miscellaneous (Gynae), Subject name: Gynaecology & Obstetrics
In early pregnancy, doubling time of beta HCG is- 
Select and explain. 
A. 24 hours, B. 48 hours, C. 96 hours, D. 2 weeks
B: 48 hours
Answer: B: 48 hours 
Explanation: 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.