Predicting Outcomes in Pregnancies of Unknown Location

Emma Kirk; Tom Bourne


Women's Health. 2008;4(5):491-499. 

In This Article

Abstract and Introduction


A pregnancy of unknown location (PUL) is a descriptive term used to classify a woman when she has a positive pregnancy test but no intra- or extra-uterine pregnancy is visualized on transvaginal sonography. Expectant management has been shown to be safe for the majority of women with a PUL. Serum progesterone and human chorionic gonadotrophin levels as well as mathematical models play a role in predicting the final outcomes of PULs, which include intrauterine pregnancy, failing PUL and ectopic pregnancy. Other possible predictors of outcome have been studied, but currently no factor has been identified that combines accuracy with reproducibility and simplicity. This article discusses the various aspects of the management of women with PULs. Future work should be aimed at prospectively testing current models in order to predict the outcome of a PUL and minimizing follow-up.


A pregnancy of unknown location (PUL) is when, in a woman with a positive pregnancy test, an empty uterus is visualized on transvaginal ultrasound scan (TVS), with no signs of an intrauterine pregnancy (IUP) or an extrauterine (ectopic) pregnancy. Whilst the majority of women will subsequently be diagnosed with spontaneously resolving pregnancies (failing PULs) or IUPs that were too early to visualize on TVS, a proportion will be diagnosed with ectopic pregnancies that were too early to visualize or were missed on the initial TVS examination.[1,2] The failing PUL group will include both failing IUP and extrauterine pregnancies, since the location of the pregnancy may never be determined. The definitive diagnosis of a woman with either a failed IUP or ectopic pregnancy has important clinical consequences, including prognosis as to the possibility of a repeat ectopic pregnancy, the need for assisted reproductive technologies or workup for potential recurrent pregnancy loss. Therefore, attempts should be made to make a definitive diagnosis when possible. A small group of women will have a persisting PUL, defined as PULs that biochemically behave as ectopic pregnancies. The serum human chorionic gonadotrophin (hCG) levels fail to decline and no evidence of the pregnancy is ever identified by TVS or laparoscopy.[2] PULs form a significant amount of the workload and risk associated with patients attending a hospital with complications in early pregnancy.

Studies report that in women attending an early pregnancy unit (EPU) with a positive urinary pregnancy test, the location of the pregnancy may be confirmed in up to 90-92% of cases on the basis of the initial TVS findings.[1,2,3] However, in practice, many more will initially have inconclusive scans and be classified as PULs outside specialist centers. Studies report that 8-31% of women referred for ultrasound assessment in early pregnancy may be initially classified as a PUL.[1,2,4,5,6] Published data demonstrate that whilst the majority of women (50-70%) will have spontaneously resolving pregnancies (failing PULs), 7-20% will subsequently be diagnosed with an ectopic pregnancy (Figure 1).[1,2,4,5,7] A quarter of women with ectopic pregnancies will initially be classified as having a PUL.[3] A study from the EPU of a London, UK, teaching hospital demonstrated that more than 90% of ectopic pregnancies may be visualized on TVS prior to treatment, with 74% being visualized on the initial TVS.[3] However, the proportion of ectopic pregnancies in the PUL population and the proportion of all ectopic pregnancies initially classified as PULs will be higher if the quality of ultrasound assessment is poor.

Figure 1.

Outcome of women attending early pregnancy units.
PUL = Pregnancy of unknown location; TVS = Transvaginal ultrasound scan.

An expectant approach to the management of PULs has been demonstrated to be safe.[1,4,5,7] However, there is no consensus on what is an acceptable intervention rate in this group.[8] Currently, women with PULs are followed up with hormone measurements, repeat TVS and possible laparoscopy or uterine curettage until a diagnosis is confirmed. Table 1 summarizes some of the recently published studies on the prediction of ectopic pregnancy in the PUL population.


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