Placental Hormones

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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. Placental Hormones and Their Metabolic Effects in Pregnancy

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 Synthesis in the Feto-Placental Unit

⭐ 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.

Practice Questions: Placental Hormones

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The role of human placental lactogen is :

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Flashcards: Placental Hormones

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Factors XI and _____ are decreased in pregnancy

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Factors XI and _____ are decreased in pregnancy

XIII

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