This happened in my first pregnancy too. Now again. No arm hairs at all - as if I'd shaved them all off - for the entire pregnancy.
Also I've got very very few leg hairs - I'm not very good about epiladying them - but have not worried about it since being pregnant as I've hardly got any hairs at all.
I just wondered if this was normal though???
Oh yes - and I've not had to pluck my eye brows either.
Arm pit hairs are still growing though ...