You can do SW while trying to get pregnant, throughout your pregancy and post-birth even while breastfeeding as it's a balanced, healthy diet and just what you need. While pregnant you need to get a permission slip from your midwife saying it's okay. You don't get any extras until after the birth and then only if you breast feed. You would get more HEs, the number depending on the age of the baby and whether you are breastfeeding exclusively or weaning.
Forgot to add you do not to eat anymore as the months go past ,for a start you get fuller quicker as your stomach becomes compressed and I think alot of people 'eat for 2' and cannot lose the weight after ,I have 4 babies lol !!
there's a girl in my class who's pregnant. she continued to lose in the earlier stages, which she was happy about. she's now at 4 months and is eating to maintain.....expecting small gains as the pregancy goes into the latter stages. good luck