I read this today:
On a Trimester Basis:
First trimester: 1 pound per month ~ (about 4lb) in the first three months.
Second trimester: 1 pound per week for the next three months ~ (12 - 14lb) in total.
Third trimester: around 1 pound per week ~ (12lb) over the last three months.
But remember, these are average figures for large numbers of women so just because your weight gain pattern is different, it doesn't mean anything is wrong.
Focus should not be so much on how much weight you are gaining
in pregnancy; but how well you are eating in pregnancy!
It is recommended that women should aim for a weight gain related to their pre-pregnancy BMI:If BMI was above 26, you should aim for a weight gain of between 15 and 25lb (7 and 11.5kg).
If BMI was between 20 and 26, you should aim for a weight gain of 25 to 35lb (11.5 to 16kg).
If BMI was less than 20, you should aim for a weight gain of 28 to 40lb (12.5 to 18kg).
I hope this answers your question?