Can sexual transmited diseases decrease the chances in getting pregnant?

Absolutely: Stds can infect your tubes, scar them and narrow the lumen. When the tubes are scarred it is difficult for the egg to pass into the uterus and get in impregnated. Also, stds can narrow the tubes so that an egg can get stuck, then get impregnated and cause a tubal pregnancy. This, my child, is no good. It can kill you because of the rupture and huge bleeding.

Absolutely: Infections can cause scarring in your belly and damage the fallopian tubes. The more serious the infection the more likely it leads to infertility. And multiple infections greatly increases the chance of infertility. Infections can also lead to painful sex and chronic pelvic pain.