I would say something to the effect of, "We are so happy to finally be home with our new baby. Most of you know he/she came into the world early, and of the challenges we had. Though we'd love to see you all and enjoy the holiday season, our biggest priority is to keep our new little one healthy, so we respectfully ask for a few things from you...
Please call us before you'd like to visit, and don't be offended if we've had a rough night and ask you to come another day or time.
Please be sure to wash your hands before touching or asking to hold the baby.
And lastly, we are acutely aware of the cold and flu season and it's impact on a tiny person. Please wait to visit if you have been exposed to anyone with a cold or illness; or even if you have the slightest sniffle.
We will not be attending holiday gatherings this year, as advised by our Dr.
Thank you for all of your support and understanding. We look forward to seeing you, and enjoying more social visits when the baby is a little older and stronger."
People will understand, and will not want to put the baby at risk no matter how much they want to see him/her or you~ Be sure to go out with your baby some though... walk and fresh air are always good for you and for them :)
Congratulations on your new sweet one~ And if it eases your worries at all, my son was born at 34 weeks, and is now a strong, healthy, brilliant, funny, beautiful 7 year old. As hard as it is now to imagine that your tiny precious baby will ever be running circles around you, I bet that will happen for you too~
Best of luck!