hCGhCG is a glycoprotein It is synthesized by syncytiotrophoblast of the placenta. hCG has 2 subunits :– α - biologically similar in LH, FSH and TSH. (i.e nonspecific) – β subunit - unique to hCG. (i.e specific)Structurally it is similar to - FSH, LH, TSH but functionally it is similar to LH ( i.e luteotropic), i.e. helps in maintaining corpus luteum. So, the main hormone which maintains activity of corpus luteum during pregnancy is hCG and in non pregnant state is LH. The half life of hCG is 36 hours. In early pregnancy the doubling time of hCG is 1.4-2 days. It can be detected in maternal serum as early as 8 days following fertilisation/day 22 of menstrual cycle/5 days before missed period by immuno assay. The level is 100 IU/L or mIU/mL around the time of the expected menses. The levels progressively rise and reach maximum levels by about 8-10 weeks/70 days/1st trimester. It then falls until about 16 weeks and remains at low level up to term. hCG disappears from circulation by 2 weeks following delivery.Action:Sustains the corpus luteum and thereby maintains the hormonal support to the pregnancy in early weeks. Stimulates the Leydig cells of the male fetus to produce testosterone and thereby induces development of the male external genitalia. Immunosuppressive action which helps in the maintenance of pregnancy.Note: In 19, I have not included option ‘c’ as correct answer, i.e. detected in serum and urine 8-9 days after ovulation because it is detected in serum 8-9 days after ovulation but not in urine. Extra Edge: Clinical implication of the measurement of hCG