Q: "... if a mother got the radiation poisoning, her baby would very likley be born with some mutation..."
A: no.
Some people (living too close to Ivankov district, Kiev region, where Chernobyl and Pripyat are located) are still experiencing thyroid problems: mostly these are hyperthyroidism and hypothyroidism, depending on one's type of hormonal/constitution status, which in turn depends on one's personal heredity/genetic inheritance. If his/her parents/grandparents suffered from thyroid problems, then most likely that he/she will be more vulnerable to this kind of issues.
Females are especially vulnerable to it due to their emotional sensitivity (Globus Pharyngeus/Hystericus is emotionally and psychologically driven, but the symptoms are physical => "a lump in a throat").
The thyroid is the most important (after pituitary gland) endocrine gland in a human body. These two glands control the rest of glands in the body, including reproductive glands. Of course, if a woman eats healthily, doesn't smoke, doesn't drink alcohol, is emotionally stable, has a stress-less job etc, she will have healthy babies (my aunt, who spent 2 weeks in Chernobyl right after the catastrophe and got hyperthyroidism, but her son is tall and huge as a buff, healthy as a horse; btw she looks ~20 years younger than her actual age - it's a family thing, but radiation didn't affect it, at least in a bad way).
It might sound like a shocking thing but some girls here in Ukraine and Belarus' do think that hyperthyroidism caused by radiation is a good thing - you get a super high metabolism, which means that the body is burning calories at a greater rate than average, and you may eat whatever you want. IMO it's better than anorexia. It's controllable.