Diagnosis of tubal ectopic pregnancy: laparoscopy versus transvaginal ultrasound

Laparoscopy is the accepted gold standard for the diagnosis of tubal ectopic pregnancy [1]. The visualization of a tubal pregnancy at laparoscopy and the subsequent histological confirmation of chorionic villi following surgery confirms the diagnosis. However, laparoscopy is an invasive procedure, not without risk, that requires general anesthetic. Furthermore, contrary to popular belief, laparoscopy does not confer 100% sensitivity for the diagnosis of tubal ectopic pregnancy [2]. Some tubal ectopic pregnancies can be missed at laparoscopy, thereby resulting in false-negative procedures. This can occur when the ectopic pregnancy is too small to be detected at laparoscopy or when the ectopic pregnancy fails spontaneously and is never seen at laparoscopy. The overall approach to the diagnosis and management of tubal ectopic pregnancy has become less invasive and more conservative. In this editorial, both laparoscopy and ultrasound as diagnostic tools in the work-up for women with tubal ectopic pregnancy are critically evaluated.

Ultrasound and, in particular, transvaginal ultrasound (TVS), has become the single diagnostic tool of choice for tubal ectopic pregnancy. Ultrasound, like laparoscopy, does not confer 100% sensitivity for the diagnosis of tubal ectopic pregnancy [3–5]; however, it is a safe, inexpensive and noninvasive test that can accurately classify the vast majority of ectopic pregnancies preoperatively [5]. The technique is well accepted by women [6] and, in trained hands, is highly reproducible. In the modern management of tubal ectopic pregnancy, laparoscopy should not be used as a diagnostic tool but rather as an operative interventional tool. In women who require surgical intervention for ectopic pregnancy, over 90% can be treated laparoscopically in a day-surgery setting [5]. There will always be a place for emergency laparotomy in a woman who is hemodynamically unstable with an ectopic pregnancy, but this is the exception rather than the rule. It is ultrasound and not laparoscopy that is the diagnostic tool of choice for the classification of ectopic pregnancy [7].

The diagnosis of ectopic pregnancy should be based on the positive visualization of an adnexal mass using TVS, rather than on the basis of a scan that fails to demonstrate an intra-uterine gestational sac. The early diagnosis of ectopic pregnancy in clinically stable women using TVS is not only potentially life saving, but may result in a decreased number of operative procedures, such as diagnostic laparoscopy and D&C [8]. The earlier the diagnosis of ectopic pregnancy in its natural history, the greater the potential for conservative management options [9], such as methotrexate or even an expectant approach. As more and more women undergo nonsurgical management of ectopic pregnancy, it will become increasingly difficult to verify the predictive value of TVS. Conservative approaches do not require histological confirmation of chorionic villi at the time of surgery and it is this confirmation that allows a unit to assess its ectopic pregnancy pick-up rates accurately. While previous studies have been able to use the gold standard to confirm the preoperative ultrasound diagnosis of ectopic pregnancy, that is, surgery with histological confirmation of chorionic villi in the fallopian tube, future studies will not. In the largest prospective study to date, which included 6621 consecutive women in an early pregnancy population, the capability of TVS when used as a single test to positively identify an ectopic pregnancy in women undergoing surgery was clearly demonstrated [5]. In this study, the sensitivity, specificity, positive predictive value and negative predictive value of TVS to detect ectopic pregnancy were 90.9, 99.9, 93.5 and 99.8%, respectively [5]. Although few clinicians would use ultrasound evidence of extra-uterine pregnancy as the primary method to diagnose ectopic pregnancies, these data suggest that ultrasound is a reliable diagnostic tool. The diagnosis of ectopic pregnancy has become more and more ultrasound based, and in particular TVS based, rather than based on laparoscopy.

Historically, the introduction of transabdominal ultrasound into gynecological practice changed the management of women with ectopic pregnancy. A positive pregnancy test in combination with the absence of an intra-uterine gestational sac on transabdominal scan became generally accepted as an indication for laparoscopy. However, such ultrasonographic appearances (e.g., the absence of an intra-uterine sac) are not specific to ectopic pregnancy. In the late 1970s and early 1980s, the nonspecific nature of not being able to visualize an intra-uterine gestational sac on transabdominal scan was well recognized [10–12]. In 1980, the discriminatory human chorionic gonadotrophin (hCG) zone was introduced and was defined as a level of serum hCG above which one should always visualize an intra-uterine gestational sac using ultrasound [10]. Thus, the probable diagnosis of an ectopic pregnancy could be made when an intra-uterine gestational sac was absent on transabdominal scan and the serum hCG level was above the discriminatory zone of 6500 U/l [10–13]. The probability of ectopic pregnancy in such circumstances exceeded 95%. In the late 1980s and early 1990s, high-resolution transvaginal probes were introduced for the assessment of pelvic pathology. This noninvasive approach to gynecological pathology was also utilized in women with early pregnancy complications. With the advent of these probes, the diagnosis of an intra-uterine gestational sac was possible at earlier gestations and the diagnosis of ectopic pregnancy became more accurate [14]. Consequently, the level of the discriminatory zone decreased [3,15–18]. If an intra-uterine gestational sac cannot be seen above the threshold value, then steps must be taken to determine whether the pregnancy is abnormal or ectopic.

When a pregnancy cannot be confirmed as intra-uterine or extra-uterine on the basis of a TVS, it is classified as a pregnancy of unknown location (PUL). The possibilities in this situation can include an early intra- or extra-uterine pregnancy that is too small to visualize on the scan, as well as complete miscarriages and self-limiting forms of ectopic pregnancy [2,19–28]. Complete miscarriages and self-limiting forms of ectopic pregnancy are also known collectively as failing PULs or trophoblast in regression [25,26,29]. PULs have also been referred to in the literature as nondiagnostic scans [30], pregnancies of uncertain site [31] or indeterminate transvaginal ultrasonography [32]. PULs are not query ectopic pregnancies and, in fact, when ultrasound skills are highly developed, only 6–14% of PULs represent ectopic pregnancies at follow-up [27,33]. Importantly, most of these PULs do not represent ectopic pregnancies, but rather failing PULs [25,26,29,31,33,34].

Screening for ectopic pregnancy with TVS in asymptomatic women at earlier gestations is not advocated [35]. It is questionable whether the possible benefits (prevention of complications and reassurance of the woman) outweigh possible disadvantages (false-positive diagnosis, financial costs and emotional stress) that could be induced by screening [36]. This policy would potentially result in more PULs, which in turn would result in an increased number of subsequent scans, visits for the woman and potential increased maternal anxiety.

Women who present with lower abdominal pain with or without bleeding in the first trimester still undergo a transabdominal scan followed by a TVS. Transabdominal ultrasonography is not diagnostic for ectopic pregnancy. Transvaginal and not transabdominal ultrasound should be the first and only approach used in women who present with early pregnancy complications. If an ectopic pregnancy cannot be seen on TVS by an experienced ultrasonographer, then there is every chance that it will not be detected at laparoscopy [37,38]. Women with clinical signs of a ruptured ectopic pregnancy who are hemodynamically compromised should not have their surgery delayed in order for an ultrasound examination to be performed.

The diagnosis of ectopic pregnancy should be based on positive visualization of an adnexal mass using TVS rather than the absence of an intra-uterine gestational sac. Although laparoscopy remains the gold standard for the diagnosis of tubal ectopic pregnancy, it is time to focus our efforts on developing ultrasound skills, such that ectopic pregnancy diagnosis is based upon pretreatment ultrasound. In clinically stable women, TVS and not laparoscopy is the tool of choice for the classification of tubal ectopic pregnancy.