I need advice!!

So basically, 2 months or so I took on a promotion (manager) of a team of 10. I’m 21 years old, recently found out I’m pregnant.

However, I have been considering turning the promotion down a few weeks before I found I was pregnant (so this isn’t the reason I’m turning down the promotion) obviously there is chance for me to return to my previous job.

I’m trying to type out an email, basically thanking them for giving me the opportunity but at the same time turning down the promotion and returning to my old position!

Any advice would be great :)