You're asking how you would know if a baby born in its seventh month was premature? That would be because normal human gestation is nine months.
What I was asking is how the OP knew it was premature. Did he know the date of conception etc. Obvioulsy paternity is a question. A normal human gestatin is 40 weeks. The baby could have also been very close to full term and had something wrong with it (low birth weight due to drugs for example)and just looked premature.. I find it odd that someone has mentioned SIDS when if it were premature...say at 29 weeks, it would have been more likely that the baby's death would be more likely a result of premature lung incapacity. Hospitals don't like to stick the term Sudden infant death syndrome on a baby when in fact the cause would be known.