Not just the fetus
The amount of radiation in simple xrays is small & unlikely to cause any issue, yet we are very sensitive to the complex changes in fetal development.
The first 4-12 wks of fetal development marks the most vulnerable period to injury & after that point we worry less. Xray exposure also adds up over time & the eggs nearby in your ovaries don't need any we can avoid. After birth, babies ready for life.