Sonography of first trimester pregnancy is a core bedside ultrasound application, and an essential component of the evaluation of patients who present with vaginal bleeding, abdominal pain, syncope or shock in early pregnancy (1). In most cases, bedside ultrasound allows emergency physicians to rapidly and accurately determine whether an intrauterine pregnancy (IUP) is present. Along with other clinical data, ultrasound findings allow emergency physicians to arrive at an accurate diagnosis and appropriate disposition, thus providing efficient care that benefits both patients and emergency department (ED) flow.

The role of emergency physicians is to rule out life threats, and as such, the primary role of bedside pelvic ultrasound in the ED is to exclude ectopic pregnancy (1). Secondary aims include the following:

Ectopic pregnancy, a common and potentially fatal condition, should be considered in all symptomatic first trimester patients who present to the ED. History and physical examination are often insufficient to reliably establish the definitive diagnosis of normal (or abnormal) pregnancy (2). Ultrasound is widely used as the most efficient and accurate means to detect and evaluate early gestations. Emergency physicians who are trained to perform and interpret bedside pelvic ultrasound should first answer the focused question: “Is there an IUP?” Ectopic pregnancy can be safely excluded in patients in whom an IUP is visualized, with the notable exception of patients who have received fertility treatments, who are at increased risk for multiple gestations and heterotopic pregnancy (3,4).

Secondary roles for pelvic bedside ultrasound include identification of abnormal pregnancies (including ectopic pregnancy and fetal demise), and detection of hemoperitoneum in ruptured ectopic pregnancy. When an IUP is not visualized, emergency physicians trained in bedside ultrasound may be able to detect specific sonographic findings consistent with ectopic pregnancy (5). Although early recognition of pregnancy loss is often not medically necessary, it remains important to advise a woman of an accurate gestational age, and when possible, to reassure her of the health of the pregnancy at the time of evaluation or to prepare her for the possibility that the pregnancy will not survive. In addition, the timeliness of appropriate follow-up care is made clearer when a viable or a nonviable IUP is detected by bedside ultrasound.

Pelvic ultrasound image acquisition for patients in the first trimester is similar to the nonpregnant patient. For a full, detailed description of the technique, please refer to Chapter 14, Figures 14.1, 14.2, 14.3, 14.4, 14.5 and 14.6. Briefly, the transabdominal view should be performed with the patient in the supine position and with a full bladder. A low-frequency probe is placed in the sagittal plane above the symphysis pubis. Using the bladder as a sonographic window, the pelvic structures—uterus, cervix, and adnexa—are visualized. The probe is then rotated 90 degrees for the transverse plane. It is important to fan up and down through the pelvis from the uterine fundus to the cervix in the transverse plane, and from side-to-side in the longitudinal plane. The transvaginal view should be performed with the patient in a pelvic bed in the lithotomy position (or with a cushion placed under the buttocks) with an empty bladder. A high-frequency endocavitary probe is placed in the vagina in the sagittal plane just past the bladder to obtain a view of the uterus in long axis. When the uterus is visualized clearly, fan through the uterus from side to side (adnexa to adnexa). Rotate the probe counterclockwise into the coronal plane. The probe should be swept, this time from top to bottom, to image the uterus from fundus to cervix. Special attention should be paid to intrauterine contents, as well as free fluid and the adnexa. In order to optimize image acquisition for first trimester pelvic scanning, select the software setting for OB to access software applications to calculate fetal heart rate and gestational age.

The specific sonographic appearance of normal pregnancy depends upon the gestational age. As the gestational age increases, the ability to assess the location and health of the pregnancy improves. Gestational age is linked to the appearance of important findings of IUP, as shown in Table 15.1.

The term abnormal pregnancy refers to a number of entities, including ectopic pregnancy, nonviable pregnancy/ embryonic demise and molar pregnancies. These pathologic entities maybe identified on the initial evaluation by ultrasound during the initial ED visit or on subsequent visits. Because the management of IUP, ectopic pregnancy, and embryonic demise differ significantly, it is important to differentiate them accurately and expeditiously. Abnormal pregnancy should be suspected when an IUP is not initially visualized on bedside ultrasound or when the normal appearance of the gestational sac, yolk sac, or the fetal heart rate is absent. Definitive diagnosis of IUP or abnormal pregnancy can be made on the initial visit with ultrasound, β-hCG levels, and surgical evaluation, or on subsequent visits. However, the emphasis of bedside ultrasound should be to identify IUP rather than abnormal pregnancy.