Subchorionic hemorrhage, during pregnancy, what is it?

No biggie generally.: Many pregnancies have sonographic evidence of subchorionic (placental) hemorrhage without ever having any adverse outcome. It can increase your chances of preeclampsia, poor fetal growth and preterm birth, though, so please see a maternal-fetal medicine specialist in your area to make sure yours is not worrisome.

Pregnancy Bleeding: A subchorionic hemorrhage/hematoma is a bleed between the pregnancy and the uterine wall. It is an US finding, that if coupled with vaginal bleeding, can potentially increase the risk of miscarriage/preterm delivery, but w/out vaginal bleeding, it's hard to say. Size matters; worse if bigger (covering ~50% of placental bed) or occurring later. It can heal itself, but you just have to wait/watch.