• Hormones – it is known that the female hormones (oestrogen and progesterone) can stimulate the growth of fibroids. This is supported by the fact that fibroids tend to occur mainly during the reproductive years when the levels of these hormones are high. 
  
• Genetics (Inherited) – there is evidence that women are 2 – 3 times more likely to develop fibroids if their mother, grandmother or sister also suffers(ed).

It is possible that the cause is a combination of these and other theories.