Subchorionic hemorrhage, a common complication in early pregnancy, can present a confusing picture on initial ultrasound scans. Visual similarities can lead to confusion with a twin pregnancy. Though an early subchorionic hemorrhage may resemble a second gestational sac, medical professionals use specific diagnostic techniques to differentiate them. This distinction is important for proper pregnancy management.
What is a Subchorionic Hemorrhage?
A subchorionic hemorrhage (SCH) is a collection of blood that forms between the uterine wall and the chorionic membrane, which surrounds the developing embryo. It results from a partial detachment. This condition is a frequent cause of vaginal bleeding during the first trimester, occurring in about 11-25% of pregnancies.
The exact causes of subchorionic hemorrhage are not always clear, though they may stem from minor vessel ruptures during implantation or early placental development. Factors that may increase the likelihood of an SCH include assisted reproductive technologies like in vitro fertilization (IVF), uterine abnormalities, or a history of recurrent pregnancy loss. Vaginal bleeding, from light spotting to heavier flow, is the most common symptom, though some individuals experience mild cramping or pelvic pressure. Many subchorionic hemorrhages are asymptomatic and are only discovered during a routine ultrasound examination.
Visual Similarities to a Twin Pregnancy
During early ultrasound examinations, a subchorionic hemorrhage can initially resemble a second gestational sac. This occurs because the blood collection often appears as a dark, fluid-filled area adjacent to the actual gestational sac. The irregular or crescent-like shape of a subchorionic hematoma can be misleading.
In very early or less clear images, this fluid collection near the developing pregnancy could be misinterpreted as another sac. This potential for confusion is heightened if the hemorrhage is located along the edge of the placenta. A subchorionic hematoma can mimic a twin gestational sac.
Differentiating Between SCH and Twins
Medical professionals rely on detailed ultrasound imaging and specific criteria to accurately distinguish a subchorionic hemorrhage from a true twin pregnancy. A key difference lies in the internal structures visible within the fluid collections. A genuine gestational sac, indicating a developing pregnancy, will contain a yolk sac and eventually a fetal pole with a detectable heartbeat.
In contrast, a subchorionic hemorrhage, while appearing as a fluid collection, will lack these embryonic structures. Sonographers look for distinct indicators such as the round appearance of a gestational sac versus the irregular or crescent shape of a hemorrhage. A subchorionic bleed also shows low-level echoes within the collection, differentiating it from the clear, anechoic (dark) appearance of an empty gestational sac. If an initial scan is ambiguous, follow-up ultrasounds are often performed to confirm the presence or absence of a fetal pole, yolk sac, and heartbeat, ensuring an accurate diagnosis.