Diagnosis and managing uncertainty

Haemodynamically unstable women with a positive pregnancy test can be assumed to have a bleeding EP. They require urgent intervention and circulating volume replacement. There is no alternative.

The diagnosis in haemodynamically stable women in early preg­nancy is commonly made by ultrasonography, supported by quanti­tative serum hCG concentration. The three most common eventual outcomes are of a viable intrauterine pregnancy, non-viable intra­uterine pregnancy (commonly referred to miscarriage), and EP. Knowledge of how the diagnosis is made for each is essential in understanding EP.

A transabdominal ultrasound scan is sometimes performed first. The woman requires a full bladder in order to obtain high-quality images. The full bladder facilitates the transmission of ultrasound waves between the body tissues and the transducer (probe) on the skin. The uterus, ovaries, and bladder can be assessed as well as more distant areas as needed such as kidneys and appendix.

A transvaginal ultrasound (TVUS) scan is used to image the uterus, ovaries, and pelvis with higher resolution. This requires the woman's consent, and privacy for her to empty her bladder and to undress. 'The transvaginal probe is covered in ultrasound gel, a probe cover, and lubricating gel. The probe is inserted into the vagina and the tip gently placed at the posterior fornix of the vagina—better resolution is obtained because the uterus and ovaries are closer to the transducer at the probe tip.

As an embryo implants and begins to grow in size it will at some point cause changes which are detectable by ultrasound. These changes occur long before any changes which would be detected by findings on clinical examination. Deviation from the progression of ultrasound findings in a normally developing intrauterine preg­nancy would strongly suggest an alternative pregnancy outcome.

Figure 39.1a shows a normal-sized uterus with a thin endomet­rium as expected in the non-pregnant female. Figure 39.1b shows a thickened endometrium in keeping with secretory phase endo­metrium or very early stages of pregnancy. The embryo if present is too small to be seen by modern ultrasound machines. Figure 39.2a shows a small sac in the endometrial cavity, which is located towards one side of the cavity. This is known as an eccentrically placed sac and is suggestive of an intrauterine pregnancy. This stage falls short of confirmation that the pregnancy is developing in the uterine cavity. The reason for this is because the sac appears empty, that is, without any other structures visible within it. An empty sac placed centrally in the uterine cavity is a ‘pseudosac' and is likely to be a small collection of blood pooling in the uterine cavity.

Pseudosacs are associated with EPs, and if misinterpreted can falsely reassure a woman with an EP that the pregnancy is intra­uterine. Figure 39.2b shows an intrauterine sac with a yolk sac. The presence of the yolk sac means that the whole intrauterine sac can now be referred to as a gestation sac. This finding means that the pregnancy is intrauterine. The stage of development is in keeping with normally developing pregnancy. A follow-up scan is required

Figure 39.1 Ultrasonography shows (a) a normal-sized uterus with a thin endometrium as expected in the non-pregnant female, and (b) a thickened endometrium in keeping with secretory phase endometrium or very early stages of pregnancy.

Figure 39.2 Ultrasonography shows (a) a small sac in the endometrial cavity, which is located towards one side of the cavity, and (b) an intrauterine sac with yolk sac. The presence of the yolk sac means that the whole intrauterine sac can now be referred to as a gestation sac; (c) a follow-up scan.

as shown in Figure 39.2c to confirm or refute viability. An additional structure, the fetal pole, is now seen in the gestation sac. Using a TVUS scan under ideal conditions, fetal heart motion can be seen when the fetal pole measures 2-3 mm in length, and this would con­firm viability. The absence of fetal heart motion with a small fetal pole may suggest miscarriage; however, it may be in keeping with very early stages of a normal pregnancy also. A repeat scan at least 7 days apart should reveal further development in the size of the gestation sac and fetal pole with fetal heart motion now visible con­firming a viable pregnancy. The absence of development, the ab­sence of fetal heart motion with a fetal pole greater than 7 mm (in the United Kingdom), or an empty uterus with a thin endometrium suggest a non-viable pregnancy (1). Guidelines for making the diag­nosis of miscarriage are designed to minimize the risk of inadvert­ently reporting an early-stage viable pregnancy as non-viable (1). The absence of a previously seen gestation sac in association with a history of vaginal bleeding strongly suggests that a miscarriage has occurred between scans and the fetal tissue has been passed through the cervix. Figure 39.2d shows a developing fetus of 9 weeks' gesta­tion within the uterus with fetal heart motion and fetal movements seen clearly during the scan.

As described previously, there is a point during the normal growth of a viable intrauterine pregnancy in which the developing struc­tures can be detected by ultrasound. This will vary between women and pregnancies. In women with technical obstacles to ultrasound such as a retroverted uterus, fibroids, or obesity, the healthy preg­nancy will only be detected at a more advanced stage when larger structures are present. This will also be the case for women in whom only a transabdominal ultrasound scan is acceptable.

Figure 39.2d demonstrates ultrasound findings with an intra­uterine pregnancy with or without fetal viability. A repeat scan after 1-2 weeks is sometimes required to allow development to demon­strate viability, or to demonstrate the lack of development associated with miscarriage.

The presence of an EP can be strongly suggested by scan find­ings of an empty uterus and either identification of an adnexal ges­tation sac, or a heterogeneous adnexal mass as demonstrated in Figures 39.3a and 39.3b. TVUS scanning can have a positive pre­dictive value of 97% and a negative predictive value of 99% in diag­nosis of EP in experienced centres (14). The presence of a small or trace amount of free fluid in the pelvis is common in early preg­nancy scanning. A large amount of free fluid in the context of a suspected EP can be assumed to be blood, and will usually warrant surgical management. Figure 39.3c shows free fluid with floating small bowel taking the irregular shape of the pelvis and pouch of Douglas.

Of stable women presenting with symptoms in early pregnancy, typically 70% will have an intrauterine pregnancy identified at the initial scan.

(15). The remainder will fall between the criteria described previ­ously where the pregnancy sac cannot be identified either within or outside the uterus. This includes women with serum hCG concen­trations above and below the discriminatory zone. The women are given the working diagnosis ‘pregnancy of unknown location' (PUL)

(16). This is an intermediate diagnosis for which further or repeat investigation is required to reach a final diagnosis or pregnancy outcome. This could be a viable intrauterine pregnancy, non-viable intrauterine pregnancy, or an EP. Around 20% of women initially classed as PUL will have an EP.