well ladies i have done loads of research on the twin front as i am a fraternal twin, which is 2 separate eggs. I would imagine tat to do this ur ovaries have to release two eggs from the same ovary or both release an egg. This is known as hyper ovulation and therefore can be passed down the female line of the family, so only females born can get it. So it is possible have the gene from my mum. I think the chances go down from 1 in 60 for most people to 1 in 20 or something for me.
As for identical twins, they are not hereditary and happen as a rare occurrence. The chance of this happening is 1 in 250.
I must admit i would love to have twins, and secretly hoping this prolonged right ovary ache is due to releasing more than one egg
xx