Chlamydia has the ability to damage the reproductive organs most often the fallopian tubes as the infection rages around. The bacterial infection damages healthy tissue and leaves scar tissue behind instead. It is no surprise, when you think about it, that scarring inside the fallopian tubes has the ability to prevent a fertilized egg from moving down into the uterus, thus causing a tubal pregnancy. Tubal pregnancies always result in pregnancy loss, and can also quickly become life-threatening for mothers. If timely treatment is not provided, the tube will rupture and the internal hemorrhage that results can easily be deadly. In many cases, the removal of the embryo from the tube will also require part of the tube itself to be removed, and can cause future infertility.
These are all compelling reasons to go through STD testing before getting pregnant, or in the early stages of pregnancy if you already conceived. If you are monogamous, and convinced that your partner is too, you could still have chlamydia if you had a previous relationship. STD testing is no more than a little bit of a hassle, but treatment could prove to be life saving.