It was true for me. I lost a bunch of weight in the beginning, and around 24 weeks started gaining it back. I'm 26 weeks today, and I've gained about 10 lbs in just 2 weeks.
I'm 20 weeks 4 days, when I first got pregnant I lost 11 pounds and now I have have only gained about 4-5 and I'm 5 months. I'm also a ftm, my doc says its nothing to worry about and that first time moms sometimes do not gain weight like others. I barely show as well, as long as your baby is healthy you're good. (: good luck!
I've only gained 7lbs so far and ill be 36 weeks Sunday.
So I don't believe that rumor to be true. Everybody is different though!