Human chorionic gonadotropin (hCG)
Also known as: hCG, β-hCG, pregnancy hormone
A glycoprotein made by the syncytiotrophoblast from implantation onwards that acts like LH to rescue the corpus luteum, keeping progesterone high until the placenta takes over — and is the hormone detected by pregnancy tests.
Overview
hCG shares its α-subunit with LH, FSH and TSH; its β-subunit resembles that of LH but has a long C-terminal extension that gives it a longer half-life (≈24–36 h) and allows specific assays (β-hCG). It is secreted by the syncytiotrophoblast as soon as implantation begins and becomes detectable in maternal serum ≈8–11 days after conception; urine tests are usually positive by the first day of the missed period.
hCG binds the LH/hCG receptor (Gs/cAMP) on the corpus luteum, preventing its regression and maintaining progesterone and estrogen secretion — essential until the luteo-placental shift at ≈7–9 weeks. In early viable pregnancy serum hCG rises rapidly (roughly doubling every ≈48 h), peaks at ≈8–11 weeks and then falls to a lower plateau. In a male fetus it also stimulates fetal Leydig cells to produce testosterone for sexual differentiation before fetal LH takes over. It has weak TSH-like activity.
- Location
Source: syncytiotrophoblast of the placenta (and some tumours). Targets: corpus luteum; fetal Leydig cells; maternal thyroid (weakly).
Function
- Maintains the corpus luteum and its progesterone secretion in early pregnancy.
- Stimulates fetal testicular testosterone production.
- Promotes placental angiogenesis and immunotolerance (local effects).
- Physiology
Class: glycoprotein (α + β). Receptor: LHCGR — Gs/cAMP. Half-life ≈24–36 h. Peak ≈8–11 weeks of gestation.
- Regulation
Production reflects trophoblast mass and is stimulated by GnRH-like signalling within the placenta; it is not under feedback control.
Clinical significance
Pregnancy diagnosis and early pregnancy problems
A suboptimal rise or plateau suggests ectopic pregnancy or miscarriage; with an hCG above the discriminatory zone (≈1500–3500 IU/L) an intrauterine sac should be visible on transvaginal ultrasound.
Gestational trophoblastic disease
Hydatidiform mole and choriocarcinoma produce very high hCG: hyperemesis, early pre-eclampsia, theca-lutein cysts and hyperthyroidism (TSH-like action). Serial hCG monitors treatment.
Tumour marker
Raised in testicular non-seminomatous germ-cell tumours (choriocarcinoma) and some seminomas; also raised in trisomy 21 in prenatal screening.
Compiled from standard anatomy and physiology references — see the Endocrine System sources. For education only; not medical advice.