Question: what are the main causes of fibroids?
Answer: Genetics (e.g., genetic mutations in the MED12, HMGA2, COL4A5/COL4A6, or FH genes)
Estrogen and progesterone.
Growth hormones.
Micronutrients, such as iron, that the body needs only small amounts of in the blood. For instance, a deficiency of vitamin D may be associated with uterine fibroids. ... 
Major stresses. 4,5