Go for it.
Eating Primal or Paleo (they're both exceptionally healthful ways of eating, Primal is just a little less strict) will NOT HARM YOUR BABY. It is probably the best gift you could give your child to eat this way yourself while you are pregnant and nursing, and to teach your child to eat according to ancestral evolutionary principles as he/she grows. Grains, especially gluten grains, are bad for you, and that's true whether you're pregnant or not.
Your health during pregnancy has a HUGE impact on the long-term health of your child. From brain development, to immune system function, to proper growth of the skull bones (which leads to not needing braces and so on later in life, as well as having good vision), EVERYTHING about your child's development will be better served by making this switch as soon as you can.
If you're worried about calcium, eat some hard aged cheese. No lactose and tons of calcium. But you will get all the minerals you need from a diverse diet of meat, fish, fowl, eggs, veggies, tubers, etc. WAY more nutritionally dense than a CW diet, way better for you and baby.
EDIT: I forgot, organs! Liver, kidney, etc. are all powerhouses of nutrition.