There is a 16 month gap between dd1 and my twin dd's. I had no problem with jealousy etc. For me as dd1 was of course still having bottles mostly when I would bf the twins I'd prepare her bottle aswell and she would lay her head on the middle of the boomerang pillow I used to feed the twins. It was Gorgeous actually as I would watch my 3 Beautiful Girls drinking their milk smile
I was lucky the twins self settled in their cot together so that gave me plenty of time with dd1.
One thing I would recommend is when baby is here to have snacks ready made for your ds for when you are bf or busy with baby. I also found getting dd1 to help with getting wipes etc for the baby made her feel special and I always praised her when she was being gentle with the twins.
Reading special books with him now about baby in mummy's tummy will also help prepare him aswell. I read a book called 'There's a house inside my Mummy' to my ds the other week which was a Great book. Talked of the changes that happen with mummy, how sometimes mummy is too tired and feels sick and then about when mummy goes to the hospital.
Mummy of 5 Gorgeous Babes smile
My newest Gorgeous Baby Boy arrived 1st January 2014 smile xxx