My cousin's first baby had two. She had a placenta that had some things the wrong way around (the details are a bit hazy, it was nearly 5 years ago!) and the baby was getting reduced rations, so he was teeny, but it didn't come up in scans for some reason. He was born at 38 weeks, but treated as prem because of his size. Her labour stopped progressing in the birth centre and she was transferred, where it was decided to do a c-section. His cord was too short to let him get out AND it was wrapped around his neck, to boot. If someone's gonna have a medical oddity, it'll be her - she has a long list of aberrations! He is fine now and there were no issues after she was discharged, but as I said, he's nearly 5 and I don't think that's long enough to be able to declare him complication-free in an evidence-based manner, but we hope it is.
Her second birth was normal, much to everyone's shock.