BeSha'ah tovah! We are happy to hear that the fetus is all right and wish you a refuah sheleimah and a safe continuation of your pregnancy.

A subchorionic hematoma is typically a sort of clot between the placental membrane and uterine wall. The halachic status of a wound (makkah) in the uterus is a matter of halachic debate. On the one hand, in theory, a makkah even in the uterus does not make a woman niddah. On the other hand, halachic authorities are hesitant to rule leniently in such cases, as it can be difficult to pinpoint the source of a woman's bleeding to a wound. For example, bleeding from detachment of the placenta is considered dam koshi. Dam koshi does make a woman niddah.

In general, a woman with bleeding from a subchorionic hematoma is considered a niddah and must immerse in the mikveh. Accordingly, if you had a stain larger than the size of a gris (approximately an Israeli shekel or US dime) on the white portion of your underwear, or if your bleeding was a "flow" and not just staining, you are niddah and should make a hefsek taharah, observe seven clean days, and immerse. If you have any difficulty with becoming tehorah, please contact us with details.

Since the laws of stains also apply to stains from placental bleeding, and to bleeding during the seven clean days, a review of our site's articles on stains, "Ketamim" and "Toilet Paper," may prove helpful.

Please don't hesitate to write back with any further questions.