Implications of Premature Birth

I ready a very interesting article this morning. http://esciencenews.com/articles/2008/09/08/premature.children.4.times.more.likely.have.behavioral.disorders
The article discusses research done in theUK on babies born the 26th week of gestation. So, this study is specifically addressing extremely pre-term babies. At age six, the extremely pre-term babies showed a higher percentage of children being hyperactive and having attention problems. The researchers did find a gender difference in behavioral problems. Boys were more likely to suffer from behavioral problems like ADHD, but girls were more likely to suffer from things like anxiety and depression due to internalizing their emotions.
One of the reasons I find this so interesting is because I was born 6 weeks early. Because I am an identical twin, it is not out of the norm for me to have been born early. I am an axious and shy person, while my twin sister is more outgoing and confident. I always wonder where the difference came about. We have the exact same DNA and went through the same experiences. We took the same classes, participated in the same activities, and we achieved very similiar grades. However, our personalities, to me, are on complete opposite ends of the spectrum. Class discussions on the implications of genetics make me wonder what causes the behavioral differences between my twin and I.