I would do what you are doing: get some accurate information and make a decision.
unfortunately, the CDC isn't too helpful:
http://wwwnc.cdc.gov/travel/notices/...a-virus-mexico cause they don't say where it has been reported in mexico.
there is good information here[/URL]:
http://www.journeymexico.com/blog/th...u-need-to-know
that includes links to self-interested but probably correct Mexican Tourism Board information.
In short, there are currently no reported cases in the State of Mexico, let alone Distrito Federale - not likely to be any unless it is from someone who returned from another area and carried the virus from that area.
I would let my wife go, pregnant or not, to Mexico City (of course, that is her hometown so I would have no way to keep from going anyway
). But, if she were pregnant, I would also make sure she uses 30% DEET repellent, wears clothes that are pre-treated with insect repellent, and then make sure she enjoys the food and drink!