A subchorionic hematoma appears on ultrasound as a crescent-shaped dark area sitting between the uterine wall and the membrane surrounding the gestational sac. It can range from a small sliver to a large collection that dwarfs the sac itself, and its exact shade on the screen depends on how recently the bleeding occurred.
The Classic Crescent Shape
The most recognizable feature is the shape. Because blood pools in the narrow space between the chorion (the outer membrane of the pregnancy sac) and the uterine wall, it naturally spreads into a curved, crescent or half-moon outline that conforms to the contour of the sac. Some hematomas look more like a wedge or an irregular pocket, especially when they’re small, but the crescent is what sonographers typically look for first.
On the screen, the hematoma sits adjacent to the gestational sac rather than inside it. It may wrap partially around the sac or collect along one edge, often near the lower portion of the uterus where blood can eventually track toward the cervix and exit as vaginal bleeding. In some cases, though, the blood stays contained and is found incidentally during a routine scan with no bleeding at all.
How the Shade Changes Over Time
The brightness of the hematoma on ultrasound tells your provider roughly how old the bleed is. Fresh blood appears bright or light on the screen (what sonographers call hyperechoic, meaning it reflects a lot of sound waves). Over the following days to weeks, as the blood breaks down and becomes more liquid, the collection gradually darkens. An older hematoma looks nearly black (anechoic), similar to the fluid inside the gestational sac itself.
This evolution means the same hematoma can look quite different from one scan to the next. A bright area that turns darker at a follow-up appointment is generally a good sign: it means the blood is being reabsorbed rather than accumulating. If a previously dark collection suddenly has a new bright region, that may indicate fresh bleeding on top of the older clot.
How Providers Confirm the Diagnosis
A few other things can mimic a subchorionic hematoma on ultrasound, so providers look at additional clues to confirm what they’re seeing. One key test is color Doppler, which maps blood flow. Hematomas have no active blood flow inside them, so they appear completely silent on Doppler. If the dark area shows blood flowing through it, it’s something else entirely, like a blood vessel or part of the placenta.
Chorioamniotic separation, a condition where the inner membrane lifts away from the outer one, can also create a dark space that looks similar. The difference is that the lifted membrane in chorioamniotic separation extends over the surface of the placenta and connects to where the umbilical cord attaches. This distinction matters because chorioamniotic separation usually resolves on its own by around 16 weeks and carries different implications than a hematoma.
Location also helps narrow the diagnosis. A subchorionic hematoma collects between the uterine wall and the chorionic membrane. A retroplacental hematoma, which is more concerning, sits behind the placenta itself. The two can overlap in appearance, but the position relative to the placenta helps your provider distinguish them.
What Size Means for Risk
Providers typically measure the hematoma and compare it to the size of the gestational sac, because relative size matters more than absolute size. A 2025 study in Frontiers in Medicine tracked IVF pregnancies with subchorionic hematomas and found a clear relationship: the larger the hematoma relative to the gestational sac, the higher the miscarriage rate.
When the hematoma was smaller than half the volume of the gestational sac, the miscarriage rate was about 11%. At 50 to 100% of the sac’s size, it rose to roughly 14%. Between 100 and 500%, about 16%. And in the rare cases where the hematoma was more than five times the size of the sac, 80% of those pregnancies ended in miscarriage. For context, most subchorionic hematomas fall into the smallest category and resolve without complications.
What Follow-Up Scans Look For
After a subchorionic hematoma is identified, your provider will likely schedule one or more follow-up ultrasounds to track its progress. They’re looking for three main things: whether the collection is shrinking, staying the same, or growing. A hematoma that gets smaller and darker over successive scans is resolving. One that stays stable is being monitored. One that grows or shows new bright areas suggests ongoing bleeding.
The timing of follow-up scans varies, but many providers check again within one to two weeks of the initial finding, then space scans further apart if the hematoma is stable or shrinking. Most subchorionic hematomas resolve by the second trimester. During these visits, the provider also confirms that the pregnancy is progressing normally by checking for a heartbeat and appropriate growth, since those factors together give a much clearer picture of overall risk than the hematoma alone.