DD was a preemie (35 weeks). I had a shortening/funneling cervix and ended up delivering due to pPROM.
I got pregnant with my DS when my DD was 7 months old. It was not "planned" per se; DD was an IVF/ICSI baby so I truly didn't think I could get pregnant without help. First month after I stopped nursing - bam - pregnant.
My pregnancy with DS was actually better. I was on a 17-P regimen and knew what to expect. I was induced at 39w4d and DS was perfectly healthy.
When I delivered my DD early I was given a "warning" too - but it was 6 months. Neither my OB or MFM (high risk) even batted an eyelash when I got pregnant so quickly. It was totally not an issue for either of them.