Preggo chicks probably stayed at home, hard to get infected then
It's likely much more complicated than that, and we won't know the real reason for a while. We do know it affects men more than women.
Somewhat unrelated. A pregnant woman who got exposed to very high, lethal levels of radiation in the 80s at Chernobyl should have had a quick, agonizing death. Instead, she survived and gave birth while experiencing little to no symptoms of radiation poisoning.
The baby died shortly after birth. She was told that her unborn baby had absorbed most if not all of the radiation like a sponge, thus saving her life. She was told too that she could never again have a baby, but she did get pregnant again and have a baby. She and her grown kid are still alive today.