It is not a rule that one should always keep on gaining weight during all visits. It may remain constant or even sometimes reduce by 1-2 kg. Total weight gain during whole pregnancy should be around 10-11 kg. In already overweight patients the weight gain should be lesser than that. You have not mentioned your height. If the fetus is growing well and the expected weight is well within normal limits, then there is no need to worry. Mother may or may not put on weight.