Describe the indications, clinical algorithm, and limitations of transabdominal US in first-trimester pregnancy pain and bleeding
Identify relevant US anatomy including the cervix, uterus, adnexa, bladder and cul-de-sac
Perform US protocol for transabdominal views of the pelvic structures including uterus and ovaries, and obtain measurement of fetal heart rate and gestational age
Recognize the relevant findings for intrauterine avoid pitfalls for missing ectopic pregnancy:

Early embryonic structures including the gestational sac, yolk sac, fetal pole, and heart
Findings of ectopic pregnancy including pseudogestational sac, free fluid, and adnexal masses

Evaluate for the presence of intrauterine pregnancy
Assess for gestational age, fetal cardiac activity, multiple gestations
Assess for free fluid exceeding an expected physiologic amount
Abdominal pain in early pregnancy or in person with uterus of childbearing age
Vaginal bleeding in early pregnancy or in person with uterus of childbearing age

Directly identifying an ectopic pregnancy (versus recognizing there is no definitive IUP)
Ovarian cysts
Fibroids
Tubo-ovarian abscess

Uterus: short axis & long axis - ensure to trace from fundus to cervix
Ovaries if visualized: short & long axis
IUP with yolk sac/fetal pole/fetus
FHR if applicable (normal fetal cardiac activity in the first trimester is 110-180 BPM)
Gestational age if applicable

Diagnosis of IUP requires the presence of a gestational sac containing a yolk sac (YS) in two planes within the endometrium which usually occurs around 5-6 weeks gestational age.

Identification of an IUP (in the absence of assisted reproductive therapy) by an emergency physician has a negative predictive value of 99.96% and a negative likelihood ratio of 0.08 for ruling out an ectopic pregnancy1

No IUP + positive pregnancy test → perform a FAST exam to evaluate for free abdominal fluid suggestive of a ruptured ectopic pregnancy (especially in patient with hypotension, tachycardia)

Liver tip has highest sensitivity to detect abdominal free fluid
Hemorrhage and free fluid may be difficult to recognize due to mixed echogenicity material in the pelvis from blood in various stages of coagulation.
Fluid in the center of the uterus can represent early gestational sac or can represent a pseudogestational sac, which is fluid caused by a decidual reaction in the center of the uterus in the setting of ectopic pregnancy.

An intrauterine sac without a yolk sac or fetal pole visualized should be termed a “nonspecific endometrial sac” to avoid any confusion about a gestation being present or not.
As many as 1 in 10 ectopic pregnancies present with a pseudogestational sac.

An eccentrically located pregnancy <5-7mm from the edge of the myometrium is suspicious for an interstitial ectopic.
Ectopic pregnancies have been documented in the literature presenting well below traditional Beta hCG discriminatory thresholds, potentially as low as 30 IU/mL. In addition, a quantitative Beta hCG level cannot be utilized to rule out the possibility of an ectopic pregnancy or clinically differentiate an ectopic pregnancy from an early IUP. All patients who present to the ED with a Beta hCG greater than zero should have an US performed.
A gestational sac in close approximation to the cervix or c-section scar should have comprehensive imaging performed.
Patients using assisted reproductive technology have a significant risk of developing a heterotopic pregnancy. ED providers should obtain a comprehensive US when evaluating these patients due to their risk of heterotopic pregnancy.

Retroverted or retroflexed uterine position can limit transabdominal exam. Providers enhance image quality by awaiting a full bladder, lying the patient flat, moving lateral to the midline, and applying gentle graded pressure.
Do not use color doppler when evaluating first trimester pregnancy – the increased acoustic output of spectral doppler ultrasound can be harmful to the early pregnancy
Detection of congenital or fetal anomalies is outside the scope of POCUS. Patients should be informed that POCUS does not supersede or replace routine obstetric care and imaging.