Placental Hormones

hCG - Pregnancy's Herald

• Structure: Glycoprotein; α-subunit (common to LH, FSH, TSH), β-subunit (unique, confers specificity).
• Synthesis: Syncytiotrophoblast.
• Functions:
  • Maintains corpus luteum → progesterone secretion. 📌 hCG 'Heralds Corpus luteum's Goodness'.
  • Stimulates fetal testicular testosterone.
  • Maternal thyroid stimulation (TSH-like activity).
• Levels:
  • Detection: Serum 6-8 days, urine 10-14 days post-conception.
  • Doubles: Every 48-72 hrs in early pregnancy.
  • Peak: 8-10 weeks (approx. 100,000 mIU/mL).
  • Nadir: ~20 weeks, then slight rise.
• Clinical Significance:
  • Pregnancy tests (detects β-hCG).
  • Ectopic pregnancy: Slower rise/plateau.
  • Molar pregnancy (GTD): Very high levels (e.g., >100,000 mIU/mL beyond expected peak).
  • Down syndrome screening: ↑ hCG in 2nd trimester.

⭐ β-hCG is highly specific for pregnancy and is used for its detection and monitoring trophoblastic diseases.

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hPL - Fetal Fuel Manager

• A.k.a.: Human Chorionic Somatomammotropin (hCS). GH/Prolactin-like structure.
• Synthesis: Syncytiotrophoblast.
• Key Functions:
  • Maternal: ↑ Lipolysis (↑ FFAs for maternal fuel); induces insulin resistance (diabetogenic, ensures fetal glucose supply).
  • Fetal: Stimulates growth (indirectly via IGFs).
  • Other: Angiogenesis; mammary gland development (lactogenic).
• Levels: Rise throughout pregnancy, proportional to placental mass.
• Clinical: Low levels may indicate IUGR/placental insufficiency (less used as a primary marker now).

⭐ hPL promotes maternal insulin resistance, shunting glucose to the fetus, and mobilizes free fatty acids for maternal energy use.

Estrogens - Uterine Growth Gurus

• Types: Estrone (E1), Estradiol (E2), Estriol (E3) (major placental estrogen).
• Synthesis: Feto-placental unit. Placenta lacks 17α-hydroxylase & 17,20-desmolase.

• Functions:
  • Uterine growth (hypertrophy, hyperplasia)
  • ↑ Uteroplacental blood flow
  • Breast development (ductal growth)
  • Cervical ripening
  • ↑ Prostaglandin synthesis
  • ↑ Myometrial contractility (late pregnancy)
  • ↑ Clotting factors
• Levels: E3 levels ↑ progressively; reflects feto-placental health.
• Clinical Significance: Low maternal serum/urine E3 associated with:
  • Fetal distress
  • Anencephaly (no fetal pituitary/adrenals)
  • Placental sulfatase deficiency

⭐ Estriol (E3) is the predominant estrogen in pregnancy, and its production uniquely depends on the fetal adrenal gland and liver, making it a marker of feto-placental well-being.

Progesterone - Quiescence Keeper

📌 Progesterone 'PROtects GESTation'

• Synthesis:
  • Corpus luteum (<8-10 weeks), then placenta (syncytiotrophoblast; from maternal cholesterol).
  • Placenta lacks 17α-hydroxylase.
• Functions:
  • Maintains uterine quiescence (↓ myometrial excitability, ↓ gap junctions, ↓ PG synthesis).
  • Endometrial decidualization.
  • Inhibits maternal immune rejection of fetus.
  • Breast development (lobuloalveolar).
  • Substrate for fetal adrenal corticosteroid synthesis.
  • Systemic smooth muscle relaxation.
• Levels: ↑ progressively throughout pregnancy.
• Clinical Significance:
  • Luteal phase defect.
  • Supplementation in threatened abortion/preterm labor (role debated but used).

⭐ Progesterone is essential for maintaining pregnancy by promoting uterine quiescence and immune tolerance.

Minor Hormones - Supporting Stars

• Relaxin
  • Source: Corpus luteum, decidua, placenta.
  • Functions: Cervical ripening, pubic symphysis relaxation, systemic vasodilation.
• Placental CRH (Corticotropin-Releasing Hormone)
  • Rises late pregnancy.
  • Functions: Implicated in parturition timing, fetal lung maturation (via fetal cortisol), uterine contractility.

  ⭐ Placental Corticotropin-Releasing Hormone (CRH) levels rise exponentially in late pregnancy and are thought to act as a 'placental clock' for parturition timing.

• Placental GH-V (Growth Hormone Variant)
  • Functions: Maternal IGF-1 regulation, ↑ maternal insulin resistance, fetal growth.
• Inhibin A & Activin A
  • Source: Placenta.
  • Functions: Inhibin A used in aneuploidy screening (↑ in Down syndrome); FSH regulation, placental development.
• Kisspeptin
  • Functions: Trophoblast invasion, placental development regulation.

High‑Yield Points - ⚡ Biggest Takeaways

• hCG (syncytiotrophoblast): Maintains corpus luteum, peaks 8-10 weeks. Basis of pregnancy tests.
• hPL (hCS): Anti-insulin action, ensures fetal glucose. Levels ↑ with placental size.
• Progesterone: Placenta takes over from ~8 weeks; maintains uterine quiescence.
• Estriol (E3): Major placental estrogen; reflects feto-placental unit health.
• Relaxin: Softens cervix and pelvic ligaments, aiding parturition.
• Inhibin A: Placental hormone, marker in quadruple screen.
• Placental CRH: Levels ↑, may time onset of labor.