hmmm, you might want to get prepared for birth as best as you can! but honestly, I do not think you need this letter at all!
as in case of an emergency the ambulance can park in the middle of the street with lights on and they get their transportable bed out.
if lack of parking would be a problem for an emergency ambulance how could they save people's life!
possibly your neighbour's might think more in this way, no???
I think it strongly depends on how much parking space is around in your street! e.g. here in central London, it could be after a long day at work, rain pouring down from the sky the only parking space you can gather near your house!