Radiation Effects on Embryo and Fetus

Radiation Effects on Embryo and Fetus

• Radiation exposure during pregnancy can have significant adverse effects on the developing embryo and fetus.
• Classic effects include:
  • Lethal effects: pre-implantation death, intra-uterine death, and neonatal death.
  • Malformations: teratogenic effects.
  • Growth disturbances.

Critical or Sensitive Stages in Prenatal Development

• Prenatal development is categorized into periods of high and low sensitivity to radiation exposure.
• Pre-implantation (days 1-10): the embryo is most vulnerable to death; either the embryo fails to implant and dies, or it survives unaffected. Embryonic cells are rapidly growing and not well differentiated.
• Organogenesis (weeks 3-7): This period is highly sensitive to radiation. A dose exceeding 100 mGy can lead to death or malformations. Embryonic tissues are differentiating into major organs.
• Growth/Fetal Stage (week 8-birth): This period is less sensitive compared to the previous periods. Higher doses of radiation in this stage can result in premature birth and growth retardation. After week 17, the brain no longer undergoes cell division and radiation exposure will not affect IQ.

Stages of Gestation

• Stages of gestation are:
  • Pre-implantation (day 1-10)
  • Organogenesis (weeks 3-7)
  • Growth/Fetal Stage (week 8-birth)
• The risk of radiation effects is highest during organogenesis.
• Weeks are gestation weeks (GW) or postconception(PC).

Progression of Exencephaly

• Exencephaly is a serious congenital disorder.
• The development of exencephaly can be tracked through ultrasound scans at various weeks of pregnancy.

Foetal Period

• During weeks 8-17, the developing brain increases neurons rapidly and these neurons move to specific parts of the brain
• This period has high radiosensitivity due to the high rate of mitotic activity
• After week 17, no further cell division occurs in the fetus' brain.
• High foetal doses (100–1000 mGy) during late pregnancy (>25 GW) are unlikely to cause malformations, as all the organs have already been formed.

Comparison of Human and Animal Data

• The comparison of human and animal data shows that the effects of radiation exposure vary at different stages of gestation.
• Prenatal and perinatal death, developmental abnormalities and growth retardation are observed during the periods of high sensitivity.
• During fetal period (weeks 8-17), the risk for adverse effects is high.

Major Events in Understanding Effects of Radiation

• Various studies have shown radiation's effect on the development and health of the individual.
• Research of survivors of the atomic bomb is important example of study.

Probability of Bearing Healthy Children

• Probability of a child being healthy without any malformations after exposure to radiation, is a function of absorbed dose.
• No significant increase in probability is seen below 100mGy (i.e., close to 97%)

X-Ray and Fluoroscopy Exposure

• Approximate fetal doses from different procedures like X-rays, CT, Fluoroscopy and Nuclear Medicine are given in table.

Explore the critical effects of radiation exposure on embryonic and fetal development. This quiz covers lethal effects, malformations, and the stages of prenatal development where sensitivity to radiation varies. Understand how timing and dosages influence outcomes during pregnancy.