I didn't vote, b/c I don't 'have' twins.
However, DS was a twin, apparently, whose twin did not develop. The midwives decided this due to a very defined second lobe on his placenta.
When I had a blighted ovum m/c in December, at 17 weeks, there appeared to be two distinct and separate placentas expelled.
I'm 14 weeks pregnant now, and we are lightly wondering, "Twins?"
As far as family history goes....on my mother's side, I'm an only child, she's an only child, her mother is an only child. Geez. I know of no twins anywhere on maternal side.
Now....on my dad's side. Paternal grandma is a MZ twin. My dad's brother's kids (my first cousins) have a load of twins, both DZ and MZ. I think there are something like 4 or 5 sets of twins among my five first cousins.
I have read that MZ is completely non-genetic. I have read that DZ has various components on my mother's side. Conversely, I have read that my father could be a contributor for various reasons and that my husband could have certain proteins in his sperm that could contribute to MZ twins. I don't what is true, but I am certainly of the opinion that I am predisposed to twins.