Answer: “Pregnant Abdominal Pain: Naughty by Nature”


This month’s case is a guest post by Dr. Carrie Ng, a 3rd year PEM fellow from Morgan Stanley Children’s Hospital in New York, NY.





This post is in response to the post: “Pregnant Abdominal Pain: Naughty by Nature

To summarize, this was a 17 year-old female with no significant PMH who presented with abdominal pain for 1 day and a positive pregnancy test. A bedside ultrasound was performed and the following image was obtained.


You see an IUP? Nope, you don’t know me.

Who sees an IUP? Oh no, that’s fluid that’s free!

Thank you to everyone who took the quiz!












There are 3 main changes during early pregnancy.

Gestational Sac

The first sign of pregnancy is a gestational sac, which appears as an anechoic (black) circle in the center of the endometrium and is seen at 4-6 weeks gestation. This is not diagnostic of an IUP because ectopic pregnancies can produce enough hormone to cause endometrial changes, a pseudogestational sac, that look very similar to a gestational sac which is seen in 10-20% of ectopic pregnancies.









Yolk Sac

Next, a yolk sac develops, which appears as a hyperechoic (white) ring that looks like a “diamond ring” or “cheerio” inside the gestational sac and is seen at 5-7 weeks gestation. This is the first definite evidence of an IUP.









Fetal Pole

Then, a fetal pole develops within the gestational sac, which appears as a hyperechoic (white) material or thickening at the margin of the yolk sac and is seen at 6-8 weeks gestation. A fetal heart rate may be visualized at this stage.









Our patient’s images did not show a definitive IUP because there was no yolk sac or fetal pole within the empty gestational sac.


Retained Products of Conception

An endometrial mass, which is visualized as heterogeneous material within the endometrial cavity, is the most sensitive (79%) and specific (89%) sonographic feature for retained POC.1 Retained POCs should be suspected if there is an endometrial thickness > 1cm after dilatation and curettage or a spontaneous abortion.










Heterotopic Pregnancy

A heterotopic pregnancy is when a patient has an IUP and an ectopic pregnancy at the same time. The chance of this happening is low in the general population (reported as anywhere from 1/3,000-1/14,000). In a patient not undergoing fertility treatment, we consider the presence of an IUP to be sufficient evidence against the diagnosis of ectopic pregnancy because the risk of having a heterotopic pregnancy is rare. However, if the patient is receiving fertility treatment, then their risk of heterotopic pregnancy is increased to ~1/100 and ruling in IUP is not sufficient. In patients undergoing fertility treatment, OB/GYN should always be consulted when they present with OB complaints in the ED.










Ruptured Ectopic Pregnancy

Our patient’s image demonstrated no definitive IUP and the presence of free fluid, which is highly suggestive of a ruptured ectopic pregnancy.











The goal of bedside ultrasonography is to diagnose an IUP.

Pseudogestatioal sacs can be differentiated from gestational sacs by their irregular shape with pointed edges and central location within the uterus.  Ectopic pregnancies can be reliably excluded in patients with a demonstrated IUP – heterotopic pregnancy remains very rare in patients who are not taking fertility agents. Findings concerning for an ectopic pregnancy include an empty uterus, extra-adnexal mass, or free fluid in the cul-de-sac. Therefore, this patient warrants an OB/GYN consult and is considered to have an ectopic pregnancy until proven otherwise.


What Next?

When there is clinical concern for a ruptured ectopic pregnancy in a hemodynamically stable patient, the next study that should be done is a Focused Assessment with Sonography in Trauma (FAST) to look for the presence of hemoperitoneum. In a retrospective study, Rodgerson et al. showed that patients with ruptured ectopic pregnancies and positive FAST exams (in Morison’s Pouch) have been associated with decreased time to diagnosis and treatment by ~2 hours.2 In a prospective study by Moore et al., free fluid in Morison’s Pouch predicted the need for operative intervention in patients with suspected ectopic pregnancies.3 Therefore, the next bedside US that should be performed in the patient is a FAST exam, which includes a Morison’s Pouch.  In hemodynamically unstable pregnant patients, it should be the FIRST study that is performed before looking for an IUP.









Free fluid in a hemodynamically unstable pregnant female

should prompt emergent OB consult.


Back to our patient…

In our hemodynamically stable pregnant patient, the next study performed after looking for an IUP was a FAST, which demonstrated free fluid in the left quadrant which was concerning for a ruptured ectopic.   In the operating room, she was found to have a ruptured ectopic pregnancy and >200 mL of blood in her abdomen. She underwent a right salpingectomy but otherwise did well.


Learn more about First Trimester OB ultrasound here or here or here.

If you want to see YOUR image included in the next Image of the Month, please email interesting stills and/or clips in addition to a small blurb on the patient to Lorraine Ng at

  1. Durfee SM, Frates MC, Luong A, Benson CB. The sonographic and color Doppler features of retained products of conception. J Ultrasound Med. 2005;24(9):1181-6-9.
  2. Rodgerson JD, Heegaard WG, Plummer D, Hicks J, Clinton J, Sterner S. Emergency department right upper quadrant ultrasound is associated with a reduced time to diagnosis and treatment of ruptured ectopic pregnancies. Acad Emerg Med. 2001;8(4):331-336. doi:10.1111/j.1553-2712.2001.tb02110.x.
  3. Moore C, Todd WM, O’Brien E, Lin H. Free Fluid in Morison’s Pouch on Bedside Ultrasound Predicts Need for Operative Intervention in Suspected Ectopic Pregnancy. Acad Emerg Med. 2007;14(8):755-758. doi:10.1197/j.aem.2007.04.010













Lorraine Ng

Lorraine Ng

Assistant Clinical Professor and the Fellowship Director of the Pediatric Emergency Ultrasound Fellowship at Columbia University Medical Center
Lorraine's academic interests are in emergency ultrasound and medical education. She is the editor for the Ultrasound Image of the Month series for PEMNetwork.
Lorraine Ng
Lorraine Ng

Lorraine Ng

Lorraine's academic interests are in emergency ultrasound and medical education. She is the editor for the Ultrasound Image of the Month series for PEMNetwork.