I think we just hear about the celebrity twins, it doesn't mean that celebrities have twins more than regular people kwim?

As for conceiving twins, we looked into this when we were trying and what we found was really interesting. There are 3 types of twins. Natural identical twins where one egg is fertilised by one sperm and then the egg splits these are same gender. Natural twins that may look very similar and many people think are identical but are not... One egg splits before being fertilised and those 2 eggs are fertilised by 2 different sperm. As sperm determines gender these can be 2 gender twins. The Olsen twins are these type of twins! Then there are non identical twins where 2 eggs are fertilised by 2 different sperm so you can have 2 of the same gender or different genders. Natural identical twins has no genetic pre determination at all, it's something that just happens so the old "twins skip a generation" thing is crap. What can run in the family is the non identical twins as they are formed by ovulating more than one egg which is a genetic trait. This is also the type that you would get from fertility drugs or IVF as they cause your body to ovulate multiple eggs.

This is what we found anyway, I'm sure there are different views out there. But if you are really keen I think many IVF clinics have a free consultation you could go to and they would give you the facts, even your OB could probably tell you