Both the developing embryo and trophoblast may be considered immunologically foreign to the maternal immune system. Many other contributing factors are implicated in sporadic and recurrent spontaneous abortions. Environment, drugs, placental abnormalities, medical illnesses, and male-related causes are noted. Ultrasound is the most accurate diagnostic modality in the confirmation of a viable pregnancy during the first trimester. Fetal heartbeat should be detected upon endovaginal ultrasound by the fifth week of gestation.
Subchorionic hemorrhage encompasses a spectrum of sonographic findings.
Subchorionic fluid can be classified in relation to gestational sac size and length of gestation. Subchorionic bleeding is present when pulsation of the subchorionic fluid is noted. Size of the subchorionic hemorrhage should be taken into consideration, as greater size relates to an increased risk of spontaneous abortion. Subchorionic fluid and bleeding, in combination with clinical bleeding, is associated with embryonic death. Also, presence of a subchorionic hemorrhage with fetal cardiac activity is associated with an increased rate of spontaneous abortion.