Early arrival

Katie
I'm just curious, for all you ladies who's Mo/Di twins made an early appearance before 37 weeks. Was there a reason for it I.e; medical reasons or where they just keen to meet you? 
I'm only 20+4 weeks with mine but my husband works away 28days rotation and will be due home when I am 34+3 for 28 days. So I am hoping to reach that point at least. 
Ps I'm 5'0" and 50kg Lee pregnancy if this makes a difference