How long before getting pregnant did you start taking prenatal vitamins?

I had two ectopic pregnancy two years apart. I was not even on any prenatal vitamins. Ectopic pregnancy is caused by a blockage of the tube. Like scar tissue or if you had an infection and it left scar tissue. I was told that my right tube was damaged so I had to make sure I was trying to get pregnant on the left side. You see one month you ovulate on the right and the next month you ovulate on the left. I had six kids. I didn't take any prenatal vitamins with my first three kids, I could not afford them. Back then they didn't have the programs for prenatal care like they do now. My kids were born healthy. My last three I did take prenatal vitamins.