EP21.28: Tubal ectopic pregnancies: what the scan describes and histology finds

Ectopic pregnancies (EPs) can be particularly difficult to accept if they appear to be developing normally anatomically. Patients can ask if an EP, especially with a fetal pole, can be transplanted into the uterus. We examined whether the presence of a measurable Crown–rump length (CRL) on scan predicted the finding of fetal parts at histology. Retrospective observational review of electronic ultrasound and results databases in a tertiary referral early pregnancy unit. Scan details of all patients with a confirmed tubal EP were compared with histology findings, where available, from 1st January 2018 - 31st July 2023. Scanning diagnosed 1420 EPs, representing 896 pregnancies. 438/1420 (30.8%) EPs were surgically managed and histology was available. A CRL was measurable in 75/438 (17.1%) pregnancies. The median CRL was 4.1mm (Range 0.9-27.6). Fetal parts were found in 23/438 (5.0%) pregnancies; 16/22 (72.7%) with CRL, 6/363 (1.7%) without CRL. A measurable CRL on scan was associated with identification of fetal parts at histology [p < 0.01, χ2 test; p < 0.01. Sensitivity 72.7 (95% CI 52.3-88.1), Specificity 85.8 (82.2-88.9), PPV 21.3 (13.1-31.5), NPV 98.3 (96.7-99.3)]. The Odds Ratio of finding fetal remains if a CRL was measured was 16 (95% CI 6.1-42.9). Most of the EPs diagnosed did not have a measurable CRL. If present, a fetal pole significantly increased the likelihood of finding fetal parts at histology. The numbers of EPs with a CRL and the size range of these CRLs is small. We are expanding our search to see if the trends demonstrated are consistent across larger numbers and bigger CRLs. Knowledge that fetal parts are identifiable in only 5% EPs may be helpful in counselling patients about the abnormal implantation site of their pregnancy.