Catch me if you scan: ultrasound diagnosis of ectopic pregnancy.

In recent years, ultrasound has become an essential tool in the assessment of women with suspected early pregnancy complications1. A large number of studies has already been published, describing the value of ultrasound in the diagnosis of ectopic pregnancy2,3. So, why write yet another review on this topic? We run a busy Early Pregnancy Unit in the area with the highest prevalence of ectopic pregnancy in the UK, which also receives many referrals from other hospitals of women with an uncertain diagnosis of ectopic pregnancy. The most interesting fact that we have learned over the years is that the majority of women referred with suspected ectopic pregnancies in fact had intrauterine ones that were either missed on ultrasound examination or misinterpreted as ectopics. This may sound surprising to many, as ultrasound diagnosis of intrauterine pregnancy is considered to be relatively simple and accurate. In many cases, ultrasound examination failed to identify a small amount of retained products of conception, due in part to inconsistencies in the sonographic diagnosis of incomplete miscarriage; this is often based on the use of arbitrary cut-off levels for endometrial thickness4. In other cases, however, sonographers were unable to decide whether a visible gestational sac represented an intrauterine or an ectopic pregnancy. In some cases with uncertain diagnosis, women had already received medical treatment with methotrexate prior to referral, leading to the loss of wanted normal intrauterine pregnancies. Another common problem is difficulty in differentiating between the various types of ectopic pregnancy. An accurate differential diagnosis is important in ectopics, as the management often differs depending on the type and exact location of the pregnancy. The purpose of this review is to summarize the sonographic criteria for the diagnosis of both intrauterine and ectopic pregnancies and to describe the principles of differential diagnosis of various types of ectopic pregnancy. We will not cover management of pregnancies of unknown location, as this issue has been covered extensively in recent publications5.