hCG is produced during pregnancy, primarily by the placental syncytiotrophoblast.
Function
Acts on LH receptors to maintain the corpus luteum.
Ensures continued secretion of Progesterone during the 1st trimester.
“Luteal-Placental Shift”: Occurs at ~8–10 weeks; placenta takes over progesterone synthesis, corpus luteum degenerates, and hCG levels peak then decline. t
Structure
α-subunit: common to hCG, FSH, LH, and TSH
β-subunit
Specific to hCG
Pregnancy tests generally detect hCG through antibodies to the β-subunit.
Types of pregnancy tests
hCG begins being produced by syncytiotrophoblast after invasion of endometrial connective tissue 6-7 days after fertilization
Serum level at 8 days is <5 IU/L, once serum is 20 IU/L this can be detected in a urine pregnancy test (~14 days following fertilization)
