Similar thing [1] happened in Berlin 9 months after Chernobyl. More babies than usual/expected were born with Trisomy 21.

[1] https://www.bmj.com/content/309/6948/158.full

Actually that is not what I searched for, but the only thing I found(after a casual search). I remember it to be more, dispersed all over the former German Democratic Republic which accounted for it, while the Bundesrepublik Deutschland didn't, or at least not at the times.