The shape of the endometrium evaluated with three-dimensional ultrasound: an additional predictor of extrauterine pregnancy.

The objective of this prospective follow-up study was to evaluate the potential utility of three-dimensional (3D) ultrasound to differentiate intrauterine from extrauterine gestations. Fifty-four pregnancies with a gestational age <10 weeks and with an intrauterine gestational sac <5 mm in diameter formed the study group. The configuration of the endometrium in the frontal plane of the uterus was correlated to eventual pregnancy outcome. After exclusion of three patients with a poor 3D-image quality the endometrial shape was asymmetrical with regard to the median longitudinal axis of the uterus in 84% of intrauterine pregnancies, whereas the endometrium showed a symmetry in the frontal plane in 90% of extrauterine pregnancies (P = 0.0000001). Intrauterine fluid accumulation may distort the uterine cavity, thus being responsible for false-positive as well as false-negative results. The evaluation of the endometrial shape in the frontal plane appears to be a useful additional means to distinguish intrauterine from extrauterine pregnancies, especially when a gestational sac is not clearly demonstrated with conventional ultrasound.