Miriam Stoppard says you should gain around 4lbs in the 1st trimester, up to 14lbs in the 2nd trimester and between 4lbs and 9lbs in the 3rd trimester - so you actually gain your most in the s2nd tri as you have (its at a rate of around 1lb per week although you could go 4 weeks with gaining nothing, and then put loads on in one week).
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