As for the causes of prematurity there are many such as:
1) Maternal age (<16yrs or > 35 yrs)
2) PIH (pregnancy induced hypertension)
3) Substance abuse
4) Infection (UTI, chorioamnionitis)
5) Placental abruption/previa
6) Multiple gestation (twins, triplets, etc...)
7) Incompetent cervix
9) Gestational Diabetes
I have read that about 60% of causes of premature birth are unknown.
Premature birth is turning into a national health crisis.
Around half a million (12%) babies are born premature every year.
Some other interesting statistics for you:
84% of preterm babies are born between 32-36 wks
10% between 28-31 wks
6% < 28 weeks
If you go to the march of dimes website you will find a ton of information on premature birth. Go to www.marchofdimes.com
Good luck on your project!