Brunnette - I would have 2 stable weeks and then a big growing week every three weeks. My weight has always been an issue as I'm very short and I went a bit mad at the beginning with the "permission" to eat. I've probably gone from 68kg at 20ish weeks to currently about mid eighties (probably creeping towards 90 based on the water in my ankles alone at the moment!!) I wouldnt' worry too much about your weight if you think you have basic nutrition going in? (in my case topped up with copious Cadburys, Magnums and with a cake chaser)