OVERVIEW
What are we looking for on POCUS in pregnant women with pelvic pain/vaginal bleeding in the ED? An IUP! Why identify an IUP? Ruling in an IUP (with a few exceptions*) essentially rules out an ectopic. The prevalence of a simultaneous IUP and ectopic (heterotopic pregnancy) is extremely low in patients that do not fall into the higher risk groups.
*patients undergoing IVF or ovulation induction or those with tubal scarring
THE BASICS
Definition of IUP on POCUS
See a gestational sac? Maybe a Double Decidual Sac Sign? That’s not enough!
If you see an anechoic (black) sac-like structure in the uterus, yes this could be the gestational sac of an early IUP…but it could also be a pseudogestational sac which is the result of hormonal stimulation by an ectopic pregnancy.
For a definitive IUP, you need to visualize AT MINIMUM a yolk sac (a hyperechoic [white] ring) within the gestational sac located in the endometrium and the surrounding myometrium must be 8mm thick or more at it’s thinnest point. If you also see a fetal pole +/- fetal heart beat, bonus!
First Trimester IUP
FHR calculation
When calculating FHR, use M-mode and position the line over the beating heart. Hit M-mode again to start recording and then hit freeze when you have a good tracing. Depending on how far along the pregnancy is you will either see dashed lines (as in the picture above, indicated by red arrows) or obvious waves. Click the button “Calculate” and the option for FHR should appear, press enter. If waves – measure from one peak to the next peak. If dashed lines – measure from the end of one line to the end of the next. FHR can be low in spontaneous abortion.
As far as measuring gestational age, you can use crown rump length, head circumference or femur length depending on what you see on US, but that’s extra info that’s not usually relevant to the emergent POCUS and won’t be discussed here.
What about the B-hcg “Discriminatory Zone?”
Historically, this is the B-hcg level above which you should see an IUP on POCUS. This term was created in the 80’s and its has some flaws.
Transabdominal Ultrasound (TAUS): 4,000-6,500 Transvaginal Ultrasound (TVUS): 1,500-2,000
- Remember, these numbers are based on the assumption that the patient has a singleton pregnancy. Multiple gestations have higher hcg levels at any given gestational age.
- MANY studies have shown that if the hcg level is above the “discriminatory zone” and no IUP is seen, this does NOT automatically equate to a diagnosis of ectopic pregnancy, especially in the hemodynamically stable patient. A study once reported a case where the patient’s B-hcg level was 6,567 (!!!) and no IUP was seen on initial US, but was later seen on a subsequent study. Patients with no IUP despite being above the “discriminatory zone” don’t automatically have an ectopic, rather they have a pregnancy of unknown location – a review article showed that 17-41% go on to have an IUP, 47-70% have a failed IUP, 8-16% have an ectopic.
- It is also important to note that there is no level of B-hcg that rules out ectopic except for 0! If the B-hcg is below the “discriminatory zone” and no IUP seen on POCUS it could still be an early IUP, but it DOES NOT rule out ectopic. That’s why we beta-book all these women.
In summary, these numbers can be used as a guide (“With that Beta I probably won’t see anything on TA, I will bring a TV probe in the room with me.”) but are by means not the end all be all.
Bobdiwala S, Al-Memar M, Farren J, Bourne T. Factors to consider in pregnancy of unknown location. Women’s Health. 2017; 2:13: 27-33.
US Findings Based on Gestational Age
| Structure | TAUS | TVUS | Approx B-hcg |
| Gestational Sac | 5.5-6 wks | 4.5-5wks | 17,00-6,000 |
| Yolk Sac | 6-6.5 wks | 5-5.5 wks | 8,000-15,000 |
| Fetal Parts | 7 wks | 5.5-6wks | 13,000-15,000 |
| Cardiac Activity | 7wks | 6 wks | 16,000-25,000 |
| Fetal Parts | >8wks | 8 wks | >29,000 |
“Can I pee first?”
TAUS is better with a full bladder (sound waves move better through fluid!). TVUS is better with an empty bladder.
Anatomy of the Female Pelvis
POCUS vs COMPREHENSIVE US
One 2016 study found that pregnant patients presenting with vaginal bleeding or lower abdominal pain who underwent POCUS had an average 43min shorter LOS compared to those you went for a Radiology Dept US.
A 2016 study found that bedside pelvic US in pregnant women with vaginal bleeding had a sensitivity of 96.0% and specificity of 93.1% for documenting IUP in women <20wks pregnant. ED POCUS had sensitivity of 88.9% and specificity of 100.0% for documenting Fetal Cardiac Activity.
Wilson SP et. al. Point-of-care ultrasound versus radiology department pelvic ultrasound on emergency department length of stay. World J Emerg Med. 2016; 7(3): 178–182.
PATHOLOGY – “That’s not an IUP!”
Image courtesy of Oark Ahmed: Cornual Pregnancy
Cornual (Interstitial) Pregnancy: an ectopic pregnancy that implants at the point of the fallopian tube that enters the uterine cavity, it is within one of the “horns” of the uterus. Note that the surrounding myometrium is <8mm.
Molar Pregnancy
Molar Pregnancy: classic US finding is the “snow storm” or “cluster of grapes” appearance within the uterus. This is the result of over-expression of the paternal chromosomes either through the loss of maternal chromosomes during meiosis or from dual implantation of a single egg. The importance of identifying a molar pregnancy is due to the fact that a complete molar pregnancy can develop into choriocarcinoma which can metastasize throughout the body.
Ectopic Pregnancy
Ruptured Ectopic Pregnancy: Free Fluid
When evaluating for an ectopic pregnancy you may not always identify that classic complex adnexal mass, sometimes you only see the secondary signs of a ruptured ectopic such as blood in the pelvis. Be sure to do a RUQ scan to look for free fluid in Morrison’s pouch (see FAST exam).