How to effectively diagnose ectopic pregnancy using ultrasound?

Keywords::

• cervical ectopic
• cesarean section scar ectopic
• diagnosis
• ectopic pregnancy
• heterotopic pregnancy
• ovarian ectopic
• tubal ectopic
• ultrasound

Over the past three decades, the diagnosis and management of ectopic pregnancy (EP) has witnessed significant change. Key developments have been a greater awareness of EPs, tertiary hospital early pregnancy units (EPUs), introduction of high resolution transvaginal ultrasound (TVS) probes and availability of accurate and rapid serum human chorionic gonadotrophin (hCG) assays. However, EP is still a leading cause of maternal mortality and significant morbidity worldwide. On the basis of the most recent figures from the UK, EP accounts for 54% of all first trimester maternal deaths [1].

TVS scan has replaced traditional laparoscopy as the ‘gold standard’ for diagnosis of EP. TVS enables visualization of an intrauterine pregnancy (IUP) at a much lower serum hCG titer than transabdominal ultrasound. Similarly, high resolution TVS has enabled the diagnosis of EP in clinically stable women, earlier in the natural history of the condition. Earlier diagnosis by TVS can reduce surgical intervention, allows for implementation of non-surgical conservative treatment options and is potentially lifesaving.

A systematically performed scan of the pelvis in early pregnancy will diagnose the vast majority of EPs at the initial scan. More than 90% of women who present with an EP can now be diagnosed reliably using TVS as a single stand-alone test [2]. Reports that read “…empty uterus, ectopic pregnancy cannot be excluded” should be a things of the past. The ultrasound diagnosis of EP should be based on the positive identification of an adnexal mass rather than on the absence of an intrauterine gestational sac [3]. Various studies have looked at the accuracy of TVS in the diagnosis of tubal EPs: In experienced units, 87–99% of tubal EPs should be visualized on TVS before treatment [2,4–8]. In most units, 75% of all EPs will be identified on the initial TVS; the remainder will be initially classified as a ‘pregnancy of unknown location’ (PUL). These women have a positive pregnancy test, no intrauterine or extra-uterine pregnancy or retained products of conception visualized using TVS. A total of 7–20% of these PULs will be subsequently diagnosed as an EP on subsequent scans [9].

Discriminatory zones are defined as the level of hCG above which an IUP should always be seen on ultrasound scan (transabdominal scan >6000 IU/ml, TVS >2000 IU/ml). Some units use similar discriminatory zones to aid in the diagnosis of EP in women classified as having a PUL. However, discriminatory zones may be altered by factors such as quality of ultrasound equipment, sonographer’s experience, multiple gestations, knowledge of patient’s risk factors and symptoms.

Transvaginal ultrasound diagnosis of tubal ectopic pregnancy

A total of 95% of EPs are located in the fallopian tube; most commonly in the ampulla followed by the isthmus of the tube. If present, a useful marker is the corpus luteum (seen as a ‘ring of fire’ on color Doppler), which is present on the ipsilateral side of the tubal EP in 70–85% of cases. A total of 60% of tubal EPs appear as an inhomogenous mass (‘blob sign’) adjacent to the ovary and moving separately to it; 20% appear as a hyperechoeic ring (‘bagel sign’) and 13% have an obvious gestational sac with a fetal pole, with/without embryonic cardiac activity. Examination of the pouch of Douglas (POD) for presence of fluid should be conducted when a tubal EP is diagnosed. Anechoic fluid in the POD may be physiological, but a ‘ground glass’ appearance is suggestive of hemoperitoneum; indicating either tubal rupture, leakage from the fimbrial end of the tube, tubal miscarriage or rupture of a hemorrhagic ovarian cyst. In the presence of hemoperitoneum, a complimentary transabdominal scan should be performed to evaluate Morrison pouch (space between Gerota fascia of the right kidney and Glisson capsule of the liver) in a supine position. If Morrison pouch is positive for blood, this equates to a minimal of 670 ml of blood in the intraperitoneal cavity [10,11].

Bilateral tubal EPs are very rare and are estimated to occur in 1:200,000 pregnancies [12].

Transvaginal ultrasound diagnosis of non-tubal ectopic pregnancy

Cesarean section scar ectopic pregnancy

Although rare (1 in 1800 pregnancies; accounting for approximately 6% of EPs in women with previous cesarean sections), the increasing rates of cesarean sections worldwide has seen an increasing number of these rare EPs. In cesarean section scar ectopic pregnancies (CSEPs), the gestational sac is located in the lower anterior myometrium but above the internal cervical os, at the level of the previous cesarean scar; in conjunction with an empty endometrial cavity. In addition, there is an absence of the ‘sliding sign’ (in a miscarriage, when pressure is applied to the cervix using the TVS probe, the gestational sac slides against the endocervical canal. This does not occur in a CSEP).

In pregnancies with previous cesarean sections, a recent study suggests that the gestational sac is more likely to implant in the posterior aspect of the uterus as well as lower in the cavity; as compared with the fundal location of implantation in utero with no previous cesarean sections. When implantation of the gestational sac occurs near to, or crosses the cesarean section scar, the diagnosis is not always clearly a CSEP. These pregnancies may be associated with placenta praevia and post-partum hemorrhage; and in some cases, may proceed to full term [13]. To date, no significant relationship of miscarriage to previous cesarean section has been established.

Cervical pregnancy

Cervical pregnancy is rare (incidence of 1 in 8600–12,400 pregnancies). The diagnosis is made on visualization of an empty endometrial cavity, a barrel shaped cervix and a gestational sac implanted below the level of the uterine arteries, that is, below the level of the internal cervical os. Similar to CSEPs, the ‘sliding sign’ is absent.

Ovarian ectopic pregnancy

Ovarian EP accounts for <3% of all EPs. Nearly a third of women present with hemodynamic instability due to rupture. The diagnosis is based on the classic description of a cyst with a wide echogenic outer ring [14]. This cystic structure does not move separate to the ovary on gentle pressure, unlike a tubal EP.

Interstitial ectopic pregnancy

These EPs occur when the trophoblastic tissue implants in the interstitial part (the area of the tube that traverses the myometrium) of the fallopian tube. The diagnosis is made when there is no IUP; and the interstitial pregnancy is surrounded by a thin myometrial mantle or continuous rim of myometrium. They are highly vascular entities with blood supply from both ovarian and uterine vessels. They tend to rupture later than tubal EPs with more profuse hemorrhage.

Heterotopic pregnancy

This condition exists when any of the above types of EPs occur in conjunction with an IUP. Although extremely rare in spontaneous pregnancies (1:10,000–50,000), the rates can be as high as 1:100 with the use of assisted reproductive technologies.

Conclusions

Diagnosis of EPs with TVS should be the standard practice in all units specializing in early pregnancy care. The early diagnosis of EP that TVS allows significantly decreases not only the mortality, but also the morbidity associated with later diagnosis and surgical options of treatment that were traditionally offered. Earlier diagnosis also enables the use of non-surgical conservative treatment options. We believe that in modern management, laparoscopy should be seen as the operative tool of choice, whereas TVS the diagnostic tool of choice, for both tubal and non-tubal EPs.

Financial & competing interests disclosure

The authors have no relevant affiliations or financial involvement with any organization or entity with a financial interest in or financial conflict with the subject matter or materials discussed in the manuscript. This includes employment, consultancies, honoraria, stock ownership or options, expert testimony, grants or patents received or pending, or royalties.

No writing assistance was utilized in the production of this manuscript.