Is there a way to conceive twins naturally?

[Darem]

Does anyone know how to conceive twins naturally - ie, without fertility treatment or because it runs in the family????

I used to babysit for twins when I was younger.
The mum was a non identical twin, although she and her sister looked very alike! Her boys were identical.

Partner is not nigerian although how he is behaving this week i would gladly swop him!

No great mystery, due to massive bad back problems after an accident, if I went into natural labour it could cripple me. Hence the question!