Why does tubal ectopic pregnancy occur?

On the other hand, this highly delicate procedure of embryo transportation depends upon the small hairy surface of tubal lining. In addition, the muscles of the fallopian tube contract and help in movement of the embryo. Also, the hairy surface of the tube has a smooth wavy movement directed by chemical signals from the embryo. Damage to the ciliary surface of fallopian tube can occur due to 

• Infections
• Toxins from smoking
• Immunological causes
• Hormonal alterations