Radiation in Pregnancy

Radiation in Pregnancy - Tiny Terrors Primer

• Embryo/fetus: high radiosensitivity. Dose unit: Gray (Gy); Equivalent dose: Sievert (Sv).
• Effects depend on dose & gestational age.
  • Deterministic effects: Threshold dose needed. E.g., malformations, growth restriction, intellectual disability (IQ ↓ with dose).
    • Threshold for malformations generally > 0.1-0.2 Gy (100-200 mGy).
  • Stochastic effects: No threshold; probability ↑ with dose. E.g., childhood cancer.
• 📌 "All-or-none" period: <2 weeks post-conception; high dose leads to death or normal development.

⭐ Fetal doses < 50 mGy (0.05 Gy) have not been associated with an increase in fetal anomalies or pregnancy loss; most diagnostic procedures are well below this level.

Radiation in Pregnancy - Timing is Everything

Radiation effects on fetus: critical dependence on gestational age & dose.

• Deterministic effects (malformations, IQ loss) unlikely < 50-100 mGy.
• Stochastic risk (cancer) ↑ with dose; no proven threshold. Risk: ~0.006%/mGy.

Radiation in Pregnancy - Numbers to Know

• Deterministic Effects (Thresholds):

  • 0-2 weeks (Pre-implantation): "All-or-none"; embryonic death if >50-100 mGy.
  • 2-8 weeks (Organogenesis): Malformations if >100-200 mGy.
  • 8-15 weeks (Early Fetal): Highest CNS sensitivity.
    • Severe Mental Retardation: threshold ~300 mGy.
    • IQ loss: ~2.5 points per 100 mGy (no practical threshold for this specific effect, linear response).
  • 16-25 weeks (Mid Fetal):
    • Severe Mental Retardation: threshold ~500 mGy.
  • Growth Restriction (IUGR): Generally >200 mGy.

• Stochastic Effects (No Threshold):

  • Childhood Cancer/Leukemia Risk: ↑ with dose.
    • Excess Absolute Risk: ~6% per Gy (0.006% per mGy).

⭐ Fetal doses from most diagnostic procedures are <50 mGy. Teratogenic effects (malformations, severe mental retardation) are generally not seen at acute doses <100 mGy.

Radiation in Pregnancy - Scan Smart Strategies

• Core Principles:
  • Justification: Benefit > Risk. Always confirm medical necessity.
  • Optimization: Lowest possible radiation dose (ALARA principle).
• Modality Choice:
  • Ultrasound (USG) & MRI: Preferred (non-ionizing). Avoid gadolinium with MRI if possible, especially 1st trimester.
• Ionizing Radiation (X-ray/CT):
  • Use only if essential and alternatives (USG/MRI) are unsuitable.
  • Minimize dose; use abdominal shielding if fetus is outside the primary beam.
• Counseling:
  • Pre-scan: Discuss risks, benefits, and alternative imaging options.
  • Post-inadvertent exposure: Estimate fetal dose. Reassure if dose is <100 mGy.
• Management (Inadvertent Exposure):
  • Fetal dose <100 mGy: Risk of malformations or pregnancy loss is negligible.
  • Termination rarely indicated for diagnostic radiation doses, especially <100-200 mGy.

⭐ Fetal radiation doses < 50 mGy are not associated with an increased risk of fetal anomalies or pregnancy loss.

High‑Yield Points - ⚡ Biggest Takeaways

• Deterministic effects (malformations, growth/mental retardation, fetal death) have a threshold dose.
• Stochastic effects (childhood cancer, heritable effects) have no threshold dose.
• Organogenesis (2-8 weeks): Most sensitive for major congenital malformations.
• Neurogenesis (8-15 weeks): Highest risk for severe mental retardation.
• Doses <50 mGy (5 rad) to fetus: No documented increase in adverse pregnancy outcomes.
• Pre-implantation (0-2 weeks): "All-or-none" phenomenon (embryonic death or normal development).
• Fetal thyroid avidly concentrates iodine from 10-12 weeks gestation.