This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Physiological changes during Pregnancy, Subject name: Gynaecology & Obstetrics
Radiotherapy is most harmful in which week of gestation: 
Select and explain. 
A. 4-16 week, B. 18-23 week, C. 28-32 week, D. All of the above
A: 4-16 week
Answer: A: 4-16 week 
Explanation: Ans. (a) 4-16 weekRef. Dutta's Obstetrics 7th ed./ 647RADIATION HAZARDS* Teratogenecity: Diagnostic range of radiation exposure (< 5 Rads) is not associated with any congenital malformation.* Oncogenecity: Dividing cells particularly in first trimester are more sensitive to injury from radiation. Diagnostic radiation with fetal exposure is associated with an increased risk of malignancy.* Genetic damage and intrauterine death* NOTE: radiation during early stage of pregnancy can damage the embroyo. This risk can be minimized by using the "10 day rule". This rule states that: "No women should be exposed to X-Ray for a non-urgent indication outside 10 days from her last period during reproductive period"