Ultrasound - Pregnancy (abdominal)

Indications

To confirm the presence of:

Intrauterine pregnancy

Consider in the following presentations in the first trimester:

Vaginal bleeding

Abdominal pain

Contraindications (absolute in bold)

Airway management or resuscitation required

Alternatives

Formal ultrasound scan

Informed consent

Medical emergency

Consent is not required if the patient lacks capacity or is unable to consent

Brief verbal discussion is recommended if the situation allows

or

Verbal consent

Less complex non-emergency procedure with low risk of complications

Potential complications

Failure to visualise structures (bowel gas, excess tissue, pain)

Failure of image interpretation (false negative or positive)

Procedural hygiene

Standard precautions

PPE: Non-sterile gloves

Area

Any bed

Staff

Procedural clinician

Equipment

Towel

Ultrasound machine and gel

Curvilinear ultrasound probe (abdominal pre-set or adjust depth to centre uterus and adnexa)

Positioning

Supine with hips flexed to relax the abdominal muscles (full bladder preferred)

Transducer placed on the lower abdomen over bladder just above the symphysis pubis

Sequence

Place transducer in the longitudinal plan (marker to head)

Identify bladder and uterus posteriorly with vaginal stripe (hyperechoic line from cervix to uterus)

Scan uterus from fundus to cervix

Fanning right and left obtaining complete view of the uterus

Locate pouch of Douglas behind uterus and examine for free fluid

Rotate into the transverse plane (marker to the right)

Scan through the uterus again from cervix to fundus

If a gestational sac is identified, assess for a yolk sac or foetal heartbeat

Scan laterally from the uterus, locate ovaries and assess for adnexal masses

Consider performing a FAST scan looking for free fluid

Post-procedure care

Clean ultrasound gel from patient

Complete clinical assessment combining results with clinical history, exam and β-hCG

Consider further assessment (gynae assessment, formal ultrasound)

Tips

Always discuss scan limit with patient (early pregnancy may not be seen even if it is present and viable)

Visualising an intrauterine pregnancy with heartbeat is often reassuring to the patient

Discussion

Patients with a positive pregnancy test and symptoms suggestive of an ectopic pregnancy can be evaluated in the emergency department by point-of-care ultrasound. This is especially useful when intrauterine pregnancy has not been previously confirmed.

Transabdominal ultrasound provides a wide field of view of the pelvis and provides good visualisation of the uterus and superior adnexa and free fluid. A transvaginal examination is out of the scope of practice for most emergency physicians, but allows a more detailed evaluation of the endometrial cavity ovaries and other adnexal structures.

The sonographic visualisation of an intrauterine gestational sac containing a yolk sac or embryo confirms intrauterine pregnancy and essentially excludes ectopic (heterotopic pregnancy is rare outside of in vitro fertilisation). If intrauterine pregnancy is not identified, this may represent normal early pregnancy below the detection threshold for transabdominal ultrasound (β-hCG <6000 mIU/ml), or an ectopic pregnancy.

Scanning the adnexa is also recommended looking for free fluid or for signs of ectopic such as extraovarian heterogeneous mass, usually representative of a haematoma at the site of ectopic implantation or echogenic ring in the adnexa surrounding an unruptured ectopic pregnancy (tubal ring sign).

Peer review

This guideline has been reviewed and approved by the following expert groups:

Emergency Care Institute

Please direct feedback for this procedure to ACI-ECIs@health.nsw.gov.au.

References

Emergency ultrasound imaging criteria compendium. Ann Emerg Med. 2016;68(1):e11-e48. doi:10.1016/j.annemergmed.2016.04.028

Roberts JR, Custalow CB, Thomsen TW. Roberts and Hedges’ clinical procedures in emergency medicine and acute care. 7th ed. Philadelphia, PA: Elsevier; 2019.

Dunn RJ, Borland M, O’Brien D (eds.). The emergency medicine manual. Online ed. Tennyson, SA: Venom Publishing; 2019.

Shipp TD. Overview of ultrasound examination in obstetrics and gynecology. In: UpToDate. Waltham (MA): UpToDate. 2020 Jun 10. Available from: https://www.uptodate.com/contents/overview-of-ultrasound-examination-in-obstetrics-and-gynecology

Dawson M, Mallin M. Introduction to bedside ultrasound: volume 1. New York NY: Apple Books; 2013.

Dawson M, Mallin M. Introduction to bedside ultrasound: volume 2. New York NY: Apple Books; 2013.

Lee R, Dupuis C, Chen B, Smith A, Kim YH. Diagnosing ectopic pregnancy in the emergency setting. Ultrasonography. 2018;37(1):78-87. doi:10.14366/usg.17044

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