Airline have their own rules about flying a pregnant pax. The rules vary from airline to airline and to a certain extent with the type(=length) of journey contemplated.
In some the limit is 32 weeks (full term is 40 weeks but you all new that didn't you). In others the limit is 36 weeks, but exceptions can be made with a supporting doctor's letter. The other thing to consider is that commercial flight insurance does not cover pregnancy without a supplement.
Now these rules are for a very good reason in that a pax delivering a baby in flight is at much greater risk and so is her baby.
So.......... these rules are there for a very good reason and only a complete idiot could consider flying a pregnant woman in a light aircraft such as a 172 (unless the journey had to be undertaken for a very good reason
as there are plenty of other even more life threatening complications that can occur at altitude with low oxygen tension and turbulence.
So if you are daft enough to fly a pgt pax, the emergency call would depend on the situation.......
Just my two pennorth.
Cusco
(the clue is in the name.)