Hi Jessir,
I agree with all the previous posts. The guide that I found most helpful and reliable is the nsw food authority.
I think it's ok for me to put the link for you in here cause its a government site.

http://www.foodauthority.nsw.gov.au/_Documents/consumer_pdf/pregnancy-brochure.pdf.

The better health Chanel website is also a reliable source of info.

Here's the best info that i found on listeria...

http://www.foodstandards.gov.au/scienceandeducation/factsheets/factsheets2005/listeriacommonlyaske3115.cfm

Initially I didn't have ham but missed it so now I have it sometimes really hot like in a pasta dish or toasted sandwich.

Hope that helps!