hCG: O Hormônio Essencial da Gravidez e Seus Muitos Papéis

Human chorionic gonadotropin (hCG) is indispensable for pregnancy establishment and maintenance. Its roles extend far beyond a simple pregnancy test marker.

Physiologic Roles

• Corpus luteum rescue: Binds LH receptor on luteal cells → continued progesterone/estradiol production until placental takeover (~10–12 weeks).
• Immunomodulation: Promotes maternal immune tolerance of semi-allogeneic fetus (Treg expansion, Th2 shift, HLA-G induction).
• Angiogenesis: Stimulates uterine vascular remodeling for placental perfusion.
• Fetal organ development: Promotes gonadal steroidogenesis (fetal testis Leydig cells → testosterone for male differentiation).
• Thyroid stimulation: Weak TSH receptor agonist → transient hyperthyroxinemia (physiological).

Production and Kinetics

• Source: Syncytiotrophoblast (placenta).
• Detectable: 8–10 DPO in blood; 10–14 DPO in urine.
• Peak: 8–10 weeks LMP (50,000–200,000 mIU/mL); then plateaus/declines.
• Half-life: 24–36 hours (critical for post-miscarriage/termination monitoring).

Clinical Utility

• Pregnancy diagnosis (qualitative).
• Viability assessment (doubling time).
• Ectopic/molar screening (abnormal kinetics).
• Down syndrome screening (combined test: hCG + PAPP-A + NT).
• Tumor marker (germ cell tumors, choriocarcinoma).

Without hCG, the corpus luteum regresses → progesterone falls → endometrium sheds → pregnancy lost. It is the hormonal linchpin of early gestation.