the thing with any weight loss system is that there is a restriction of calories to help you to loose weight and when your body is creating new life I don't think it is a good idea to limit what you eat. I think it is important to be aware of what you are eating and listen to your body, know when you are hungry as opposed to say bored/upset etc....

You can still apply the principles of WW and make sure you are choosing healthy filling foods (salad on wholegrain bread for instance) as oppose to chips etc.... this way you are giving your body everything it needs without going crazy and having a lot more work to do once baby is here.

Hope that make sense