I'm having a girl and have only put on 10kgs at 32 weeks, so i think that theory might be blown up!!!!
As for weighing yourself daily, i suggest you dont, its not healthy for your mental state, just leave it to once a week or fortnightly. You are pregnant, you are going to gain weight. If you exercise regularly and eat healthy, like caro said, then you will put on as much weight as you need to and everyone is different.
At 20 weeks I was about 4kgs heavier and then have gained the rest since. Dont stress too much. Good luck
Melissa