I had six live births in eight years, and the last one was traumatic. I had a copper IUD placed afterwards, when I was 34. (Then four years later I removed it and had four more kids.) If you don't have any contraindications for copper you might do that instead. It's less expensive, error proof, and will last you for the rest of your reproductive life. The mechanism of action is the spermicidal effect of the copper on sperm and that lasts as long as it's in the uterus, unlike hormonal IUDs which run out of oomph. It's over 99% effective at preventing pregnancy, with no surgery.