I think you need to have your Midwife's permission to carry on with Slimming World while you ate pregnant. IIRC it is the only diet plan that the Royal College of Midwives recommends you follow while you are preggers, cos it promotes healthy eating and a balanced diet instead of saving all your allowances for bad food and wine! Speak to your consultant when you go to join.
Good luck with trying for your baby, and good luck with SW! It really does work, I've lost my baby weight and my DS is 20 weeks.