Overlapping imaging features between miscarriage of a low-lying gestational sac and cervical ectopic pregnancy

Early pregnancy ultrasound must satisfy objective criteria to make a safe diagnosis of miscarriage. The differential diagnosis of low-lying gestational sac includes cervical stage of miscarriage and cervical and caesarean scar ectopic pregnancies. Misdiagnosis can lead to significant maternal morbidity. We describe a pregnancy in a 36-year-old primiparous woman where ultrasound findings of a low-lying gestation sac satisfied criteria for miscarriage; however, dilatation and curettage of pregnancy contents resulted in brisk cervical bleeding. Ultrasound at 6 weeks 6 days of gestation showed an intra-uterine pregnancy of uncertain viability. Repeat scan after 11 days confirmed miscarriage based on an absence of interval progression between scans and no embryonic heartbeat. The collapsed gestational sac (GS) was seen at the level of the internal os with decidual reaction and peri-trophoblastic blood flow. Inferior to the sac, minimally vascular trophoblastic appearing tissue was beginning to distend the upper cervical canal: the sliding sign was positive for the GS and negative for the upper cervical contents. Cervical stroma was clearly seen circumferential to the distending tissue. The patient underwent dilatation and curettage of the uterus complicated by 2000 ml haemorrhage requiring blood transfusion and medical and surgical management with intra-cavitary placement of a Foley catheter. Histopathology confirmed pregnancy tissue with the disruption of cervical epithelium but no true invasion. The patient was counselled to attend a specialist obstetric imaging facility for an early dating ultrasound in future pregnancies. The current body of literature does not describe cases of low-lying gestation sac miscarriage with high-risk features of trophoblastic extension into the cervical canal. We suggest maintaining a high index of suspicion and excluding differential diagnoses as the majority of women have no risk factors for ectopic pregnancy. These cases should be recommended for surgical management.