In a recent article in the Journal of Ultrasound in Medicine (through AIUM), a study was done that illustrates exactly what we all experience in practice – an ectopic pregnancy can occur at any beta hCG level….AND a normal pregnancy can result despite a higher bHCG and no IUP seen. The conversations with the radiologists who still believe in “screening” who should and should not be scanned based solely on the beta hCG level will minimize – so we hope. The lowest beta hcg I have ever seen with a diagnosed ectopic? Brace yourselves…….152 ! There have been other case reports and cohort multi-site studies that you can read here, here, here, and here about low hCG and diagnosis of ectopic pregnancy. ACEP even has an article on it. But what if the beta hCG is high? …and you see nothing in the uterus on your ultrasound? There was a study done in 2011 by Wang, et al out of UCSF that discussed this too, asking if we should increase the discriminatory zone. There are also studies that show if you DO see something in the uterus, what does that mean in relation to ectopic pregnancy? Well, first, let’s talk physiology – Now, hCG is made by the syncytiotrophoblasts of the placenta after fertilization occurs, and correlates with the size and developing of the fetus…. well, Im going to stop there, as the only reason I stated that was to type “syncytiotrophoblasts” as I rarely have the opportunity to do so (insert sarcasm).
There is, however, a term used to describe the maternal serum hCG level above which a gestational sac should be consistently visible on transvaginal sonography – “discriminatory zone” – coined in the 1980s (yup, that’s right, 30 years ago!). This was thought to be 1,000, 1,500, or 2,000 on transvaginal ultrasound (and 3,600 or 6,000 on transabdominal ultrasound) depending on the study you read. So, if the hCG is above that zone and no IUP is seen – then you have yourself an ectopic pregnancy ….until proven otherwise! – and doctors would think treating for ectopic is the appropriate next step. Then there was a hiccup – There was a study that showed an HCG of 2,000 may not mean ectopic as 33% of the study’s subjects had a normal IUP after having no IUP on ultrasound when they were above that discriminatory zone. Oopsy! But, the prior studies all kinda had a possible gestational sac, but defined an IUP as the presence of a double decidua sign or yolks sac. So, this study wanted to know if there was no gestational sac and the bHCG was above this discriminatory zone, will there be an IUP, and if so, then what is the prognosis – in other words, is this discriminatory zone be valid?
“Objectives—The human chorionic gonadotropin (hCG) discriminatory level—the maternal serum β-hCG level above which a gestational sac should be consistently visible on sonography in a normal pregnancy—has been reported to be 1000 to 2000 mIU/mL for transvaginal sonography. We assessed whether a woman with a β-hCG above 2000 mIU/mL and no intrauterine fluid collection on transvaginal sonography can subsequently be found to have a live intrauterine gestation and, if so, what the prognosis is for the pregnancy.
Methods—We identified all women scanned between January 1, 2000, and December 31, 2010, who met the following criteria: serum β-hCG testing and transvaginal sonography were performed on the same day; β-hCG was positive and sonography showed no intrauterine fluid collection; and a live intrauterine pregnancy was subsequently documented. We tabulated the β-hCG levels in these cases and assessed pregnancy outcome.
Results—A total of 202 patients met the inclusion criteria, including 162 (80.2%) who had β-hCG levels below 1000 mIU/mL on the day of the initial scan showing no intrauterine fluid collection, 19 (9.4%) with levels of 1000 to 1499, 12 (5.9%) 1500 to 1999, and 9 (4.5%) above 2000 mIU/mL. There was no significant relationship between initial β-hCG level and either first-trimester outcome or final pregnancy outcome (P> .05, logistic regression analysis and Fisher exact test). The highest β-hCG was 6567 mIU/mL, and the highest value that preceded a liveborn term baby was 4336 mIU/mL.
[Also: "Comparing outcomes in cases with β-hCG below 1000 versus above 1000 mIU/mL also showed no significant difference: 89.9% (125 of 139) live at the end of the first trimester in the low hCG group versus 88.6% (31 of 35) live in the high hCG group; 86.6% (110 of 127) liveborn in the low hCG group versus 80.6% (25 of 31) liveborn in the high hCG group (P > .05 for both comparisons Fisher exact test)]“
Conclusions—The hCG discriminatory level should not be used to determine the management of a hemodynamically stable patient with suspected ectopic pregnancy, if sonography demonstrates no findings of intrauterine or ectopic pregnancy.
New Guidelines published in NEJM in Oct 2013 have changed the criteria in order to reduce the risk of prematurely stating a pregnancy is non-viable.
A great discussion on this also heard here BroomeDocs’ Casey Parker: here
For a great 5 minute talk on Ectopic pregnancy and how to identify it by ultrasound, see Dr. Phil Perera’s Soundbytes insert – but, as the studies above suggest, if you see no IUP despite an hCG above the discriminatory zone, there may not be an ectopic pregnancy – make sure to look around the adnexal region, and have close follow up with the Ob/Gyn doctor.