Firstly I am in contact with my vet on this matter but wanted an opinion from here...

My bitch is pregnant with her first litter and is on day 48 today, last night she lost her mucus plug and this morning her temp dropped to 37.2 from 37.9 but showing no other signs thank goodness however should I be concerned about premature birth?

What is your experience with reliability in temps? How much before labor commences is mucus plug normally?

Thank you

My bitch started loosing her plug around a week before she had them.
I dont think that temp drop is low enough, mine normally go under 37, and near abouts 36.5. Their temps go up and down and if i have a low temp i take it again about 5 mins later to check as sometimes the it was just an odd reading.
I wouldn't panic and keep an eye on her.

That temp drop doesn't sound low enough to worry. I stopped temp taking in my bitches now but when I used to do it it would drop under to 36's approx 6 to 12 hours before starting.

Thank you :)