From the Guidelines
Transvaginal ultrasound (TVUS) is the best imaging modality to rule out ectopic pregnancy. This is based on the most recent and highest quality study, which states that TVUS is currently considered the single best diagnostic modality to assess for ectopic pregnancy 1. The study highlights that a combined transabdominal and transvaginal approach is typically used for pelvic US imaging, and both should be performed when possible. TVUS is the most useful method to evaluate the endometrium, early pregnancy, and adnexa.
Some key points to consider when using TVUS to rule out ectopic pregnancy include:
- The sonographic detection of a normal intrauterine pregnancy at b-hCG levels >2,000 mIU/mL can be complicated by obscuration of the endometrial cavity by fibroids, hemorrhage, intrauterine devices, or vaginal bleeding 1.
- The absence of an intrauterine pregnancy when the b-hCG level is >3,000 mIU/mL should be strongly suggestive (but not diagnostic) of an ectopic pregnancy 1.
- TVUS as a screening test for ectopic pregnancy demonstrated a 99% sensitivity and 84% specificity in a prospective study of 1,427 patients with b-hCG levels >1,500 IU/L 1.
- A meta-analysis of 14 studies with 12,101 patients with ectopic pregnancy showed a positive likelihood ratio of 111 for the finding of adnexal mass without an intrauterine pregnancy on TVUS, making TVUS the single best diagnostic modality for evaluating patients with suspected ectopic pregnancy 1.
In terms of diagnostic accuracy, TVUS has a high sensitivity and specificity for detecting ectopic pregnancy, with a sensitivity of 99% and specificity of 84% in a prospective study of 1,427 patients with b-hCG levels >1,500 IU/L 1. Additionally, the procedure should be combined with quantitative serum beta-hCG levels for optimal diagnostic accuracy. If the beta-hCG is above the discriminatory zone (typically 1,500-2,000 mIU/mL) and no intrauterine pregnancy is visible on transvaginal ultrasound, an ectopic pregnancy should be strongly suspected. In indeterminate cases, serial ultrasounds and beta-hCG measurements may be necessary. Other imaging modalities like CT or MRI are rarely indicated for initial evaluation of suspected ectopic pregnancy due to radiation exposure concerns, cost, and limited additional diagnostic value.
From the Research
Imaging Modalities for Ruling Out Ectopic Pregnancy
- Transvaginal sonography (TVS) is the imaging modality of choice for diagnosing ectopic pregnancy, with overall reported sensitivities of >90% 2.
- TVS has been shown to have higher diagnostic accuracy and lower misdiagnosis rates compared to transabdominal ultrasound (TAS) 3.
- The definitive diagnosis of ectopic pregnancy can be made with ultrasound visualization of a yolk sac and/or embryo in the adnexa 4.
Diagnostic Criteria
- Diagnosis of ectopic pregnancy should be based on positive visualization of an ectopic pregnancy rather than the inability to visualize an intrauterine pregnancy 2, 5.
- Specific sonographic criteria exist for the diagnosis of tubal and non-tubal pregnancies, including cervical and caesarean section scar pregnancies 2.
- The presence of mixed ectopic masses, adnexal masses, ectopic gestational sacs, and visible embryo and fetal heart in the ectopic sac shadow can be detected using TVS 3.