emDOCs Podcast – Episode 136: Ectopic Pregnancy Myths Part 2

Myth 5: Ectopic Pregnancies Demonstrate Reliable Trends in Serum β-hCG Levels.

• Much of our normal practice is to follow serum β-hCG levels in patients with a pregnancy of undetermined location. 
• A small study showed viable IUPs had an increase in serum β-hCG by at least 66% in 48 hours. As the initial β-hCG level increases, the rate of increase over 48 hours decreases (Kadar). 
  • We expect an increase of at least 40% if the patient has an initial β-hCG level of 1,500 to 3,000 mIU/mL (1,500 to 3,000 IU/L) and 33% for an initial β-hCG level greater than 3,000 mIU/mL.  
  • If there is an increase of less than these numbers, that suggests an abnormal pregnancy. 
  • ACOG guidelines state an increase in serum β-hCG under 53% in 48 hours suggests an abnormal pregnancy (ACOG).
• Problem: Up to one third of pregnancies will not demonstrate this change in β-hCG levels, and there is overlap between normal pregnancies, nonviable pregnancies, and ectopic pregnancies with β-hCG changes (Seeber). 
• Ectopic pregnancies can have β-hCG levels that decrease, remain stable, or rapidly increase, but they can also have an increase in β-hCG that could be considered “normal” (Morse, Silva, Barnhart, Dillon). 
  • One study found 60% of patients with ectopic pregnancies had increasing β-hCG levels, and over 20% had a level that increased by at least 53%. Another study found that 27% had levels increasing that resembled a normal pregnancy (Dillon). 
• Takeaway: Serum β-hCG levels cannot accurately diagnose ectopic pregnancy alone; further testing is necessary.  

Myth 6: If a Pregnant Patient Has a Serum hCG Above the Discriminatory Zone and No Visualized Intrauterine Pregnancy on Ultrasound, Then an Ectopic Pregnancy Must Be Present.

• Discriminatory zone: lowest serum β-hCG level where ultrasound (US) should detect visible signs of early pregnancy (yolk sac or fetal pole) (Connolly). 
  • Level used to be 6500; it is now somewhere between 1000-3000 with our improved US and our techniques (Barnhart 1994, Kadar, Mehta).  
• Goal in the ED with a pregnant patient is to determine whether there is a viable IUP. If we do not see a fetal pole on US in the uterus and the β-hCG level is over the discriminatory zone, the patient has a pregnancy of unknown location (PUL).  
• Takeaway: If the patient has a PUL, it could be a viable IUP, a non-viable IUP, or an ectopic pregnancy. 
  • A single β-hCG level and an inconclusive US are not predictive of definitive IUP or EP. 
  • There is a lower likelihood of a viable pregnancy if the β-hCG is above the discriminatory zone and an IUP, but that the patient can still have an IUP. These patients need follow up and repeat β-hCG and US. Consult OBGYN if for follow up. If that’s not a possibility, have the patient follow up in 48 hours for repeat β-hCG and US, and give close return precautions. 
  • If the patient is unstable, obtain access and perform a FAST exam. If positive and the woman is reproductive aged,  and there is no trauma, think ectopic pregnancy consult OB to get the patient to the OR. If no OBGYN, talk to surgery.  

Myth 7: If the Serum β-hCG Level Is Less Than DZ, Then US Is of Little Utility.

Myth 8: A Ruptured Ectopic Pregnancy Cannot Be Possible if a Patient Has a Low or Even Negative Serum or Urine β-hCG Test.

• Do not rely on the discriminatory zone threshold for US.  
  • Studies have found that ectopic pregnancies can be seen on US no matter the β-hCG level. 
  • One study found confirmed ectopic pregnancies on US with β-hCG levels that ranged between 41 to 60,000 mIU/mL; over 20% had levels less than 1000 mIU/mL (Adhikari). 
  • Other studies have found that confirmed ectopic pregnancy can occur with levels less than 20 mIU/mL (even 0) (Simsek, Connolly). 
  • ACEP clinical policy provides a level B recommendation stating to obtain a transvaginal US in patients who have β-hCG levels below the discriminatory zone and concerning signs and symptoms (Brown).
• A low β-hCG or negative urine test does not rule out an ectopic or a ruptured ectopic pregnancy. 
  • Rupture may occur with levels less than 1000 mIU/mL.
    • There are numerous case reports of patients with β-hCG levels less than 10, or negative point of care testing, with ruptured ectopic pregnancy (Fu, Hochner, Grynberg, Resta). 
  • One study found 11% had β-hCG levels less than 100 mIU/mL, and close to 40% had levels between 100-999 mIU/mL (Saxon). 
  • Another study found no difference in the range of β-hCG levels in ectopics that had rupture and those that had not (Galstyan). 
• Takeaway: There is no single β-hCG level or trend in β-hCG levels that can predict rupture. There is no correlation between β-hCG levels and the risk of rupture. 
• If concerned about ectopic pregnancy, obtain an US. If the patient is unstable and a reproductive aged female, has a positive FAST, and no trauma, then assume ectopic until proven otherwise. Resuscitate and consult OBGYN. 

Summary:

• Many patients with ectopic pregnancy do not have even one classic predisposing risk factor. 
• Overall, contraceptives protect against ectopic pregnancy because they prevent pregnancy. 
• Patients with ectopic pregnancy may or may not present with pain or adnexal tenderness. 
• While rare, patients with ectopic pregnancy have been found to have initial negative urine point-of-care β-hCG tests. 
• Patients with ectopic pregnancy do not demonstrate reliable trends in serum β-hCG levels.
• Pregnant patients with serum β-hCG levels greater than the discriminatory zone and no visualized IUP on US may or may not have an ectopic pregnancy.
• If the serum β-hCG level is less than discriminatory zone, obtain US.  Ectopic pregnancy with a mass may still be found.
• Patients with a ruptured ectopic pregnancy can have low negative serum or even negative urine β-hCG tests.

Algorithm:

References: 

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