The association between 3-D transvaginal ultrasound markers and pregnancy of unknown location outcome: a pilot study.

OBJECTIVES: To assess the accuracy of three-dimensional (3D) transvaginal ultrasound (TVS) parameters in predicting the evolution of a pregnancy of unknown location (PUL).

METHODS: Prospective observational study performed at the Early Pregnancy Unit of a University Hospital from Sep-2008 to Jun-2012. Women with a positive pregnancy test without any signs of intra- or extra-uterine pregnancy at their first TVS scan were considered eligible and a 3D dataset containing the entire uterus was acquired. One experienced observer analyzed all the 3D datasets for assessing the following parameters: endometrial thickness, volume, mean gray-scale index (MGSI), and asymmetry. Women were followed until they were classified in: 1) Non-visualized pregnancy loss (NVPL); 2) Intrauterine pregnancy (IUP); and 3) High risk of complications, including both ectopic pregnancy (EP) and persistent PUL. We compared the values for these parameters observed in the three groups. We also assessed the area under receiver operating characteristic curve (AU-ROC) of these 3D TVS parameters comparing to that observed by serum β-hCG ratio (48 h/baseline) to predict PUL outcome. Then we evaluated whether combining the 3D TVS parameters would be able to improve the predictive accuracy of serum β-hCG ratio to predict PUL outcome by performing a regression analysis.

RESULTS: During the period, 4,939 consecutive pregnant women presented at the unit for their initial TVS and 325 (7%) were classified as a PUL. From those, 161 women were included in this study and had a 3D dataset of the uterus; however 19 were excluded from the final analysis because of incomplete follow-up. Therefore, data from 142 women with PUL were included in the analysis and the outcomes of these women were: NVPL = 98 (69%), IUP = 27 (19%), EP + p-PUL = 14 + 3 = 17 (12%). Endometrial thickness, endometrial volume and the proportion of endometrial shape asymmetry were significantly different among the different outcomes. The best single parameter to predict the different outcomes was the β-hCG ratio. Regressions analysis demonstrated that endometrial volume and endometrial shape asymmetry significantly contributed to β-hCG ratio in predicting of IUP, but not NVPL.

CONCLUSIONS: 3D TVS markers have a low diagnostic accuracy in predicting PUL outcome, however endometrial thickness and volume could be used as reasonable predictors of both NVPL and IUP, while endometrial shape asymmetry and MGSI could be used as reasonable predictors of IUP only. Combining endometrial volume and endometrial shape asymmetry improve the accuracy of β-hCG ratio in predicting IUP.