Early labor?

Laura • January 2012 👰🏻 January 2013 👧🏼 being induced 7/19 2016 👶🏻
So this is a very ignorant question, but I keep getting curious and anxious thinking about going into early labor. I am reading all these mommas posts about having their babies so early (31 weeks, 34 weeks...) and thank God and NICU nurses they all seem to be doing well. But my question is...
Can this happen to any momma, or is there usually an underlying issue that may cause a woman to have her baby so early?