How to diagnose and rule out abdominal (ectopic) pregnancy?

From the Guidelines

To rule out abdominal pregnancy, a transvaginal ultrasound (TVUS) should be performed as the primary imaging modality, as it is considered the single best diagnostic modality to assess for ectopic pregnancy, including abdominal implantation, with a high sensitivity and specificity, as demonstrated in a prospective study of 1,427 patients with b-hCG levels >1,500 IU/L, showing a 99% sensitivity and 84% specificity 1.

When evaluating a patient for suspected abdominal pregnancy, it is crucial to start with a thorough clinical evaluation, including a detailed history and physical examination, to identify risk factors such as previous ectopic pregnancy, pelvic inflammatory disease, or tubal surgery. Laboratory tests, including serial quantitative beta-hCG measurements, should be ordered to assess pregnancy progression. Abnormal rises in beta-hCG levels, typically less than 66% increase over 48 hours, may suggest ectopic pregnancy, including abdominal implantation.

The use of TVUS is supported by recent guidelines, which suggest that a combined transabdominal and transvaginal approach is typically used for pelvic US imaging, and both should be performed when possible 1. TVUS is particularly useful for evaluating the endometrium, early pregnancy, and adnexa, and it is currently considered the single best diagnostic modality to assess for ectopic pregnancy, including abdominal implantation 1.

Some key points to consider when using TVUS to rule out abdominal pregnancy include:

• The presence of a gestational sac using TVUS is typically correlated with b-hCG levels of 1,000 to 2,000 mIU/mL, but the sonographic detection of a normal intrauterine pregnancy can be complicated by various factors, such as 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 of an ectopic pregnancy, including abdominal implantation 1.
• Adnexal findings suggestive of ectopic pregnancy, such as the classic “tubal ring,” have a high specificity, and TVUS has been shown to have a positive likelihood ratio of 111 for the finding of adnexal mass without an intrauterine pregnancy 1.

In cases where TVUS findings are inconclusive, but beta-hCG levels are above the discriminatory zone (typically 1500-2000 mIU/mL), additional imaging such as MRI may be considered for better soft tissue visualization. Diagnostic laparoscopy may also be necessary in cases where diagnosis remains uncertain despite these measures. Prompt and accurate diagnosis is crucial for patient safety, as abdominal pregnancies are rare but dangerous, representing less than 1% of ectopic pregnancies with high maternal mortality risk.

From the Research

Ruling Out Abdominal Pregnancy

To rule out abdominal pregnancy, the following steps can be taken:

• Use transvaginal sonography (TVS) as the imaging modality of choice for the diagnosis of ectopic pregnancy, including abdominal pregnancy 2, 3
• Look for specific sonographic criteria for the diagnosis of ectopic pregnancy, including the visualization of an ectopic mass rather than the inability to visualize an intra-uterine pregnancy 2
• Check for the presence of an adnexal mass in the absence of an intrauterine pregnancy on transvaginal sonography, which has a high positive likelihood ratio (LR+) for ectopic pregnancy 3
• Evaluate the patient's history, physical examination findings, and laboratory results, including quantitative serum human chorionic gonadotropin (hCG) testing 3, 4
• Consider the potential pitfalls in diagnosing ectopic pregnancy, including reliance on beta-human chorionic gonadotropin, pseudogestational sac, interstitial pregnancy, and heterotopic pregnancy 4

Diagnostic Criteria

The diagnostic criteria for ruling out abdominal pregnancy include:

• The absence of an adnexal mass on transvaginal sonography, which decreases the likelihood of ectopic pregnancy 3
• The presence of an intrauterine pregnancy on transvaginal sonography, which rules out ectopic pregnancy 2, 3
• A negative result on quantitative serum human chorionic gonadotropin (hCG) testing, which may indicate a low risk of ectopic pregnancy 3, 5

Imaging Modalities

The imaging modalities used to rule out abdominal pregnancy include:

• Transvaginal sonography (TVS), which is the imaging modality of choice for the diagnosis of ectopic pregnancy 2, 3
• Transabdominal ultrasound, which may be used in conjunction with TVS to evaluate the patient's pregnancy 4
• Bedside transvaginal ultrasound, which can be used in the emergency department to diagnose ectopic pregnancy 5