I read it from a mainland book, so I think the following figure is for Chinese women.
Pregnant 1-3 months:
normal: 1-2 kg
rather low: <1 kg
rather high: 2-3 kg
Pregnant 4-6 months:
normal: 5 kg
rather low: <3 kg
rather high: 6-7 kg
Pregnant 7-9 months:
normal: 5-6 kg
rather low: <3 kg
rather high: 6-7 kg
Total:
normal: 12-13kg
rather low: 7kg
rather high: 14-16 kg
Besides, I read it somewhere:
Some women vomit and has no appetite at the first 3 months, so some women even get lighter then before pregnancy at the first 3 months. If the reduced amount is less than 5 %, there should be no problem.