Is a Hida (Hepatobiliary Iminodiacetic Acid) scan safe for a pregnant patient in their 2nd semester?

HIDA Scan Safety in Second Trimester Pregnancy

HIDA scans should generally be avoided during pregnancy, but when clinically necessary for urgent biliary evaluation (such as suspected acute cholecystitis or choledocholithiasis), they can be performed with appropriate precautions, as the radiation dose is typically below the threshold associated with fetal harm. 1, 2

Preferred Imaging Approach in Pregnancy

• Ultrasound is the first-line imaging modality for all suspected biliary disease in pregnant patients, as it is safe, radiation-free, and highly accurate for detecting gallstones and biliary obstruction 3
• The American College of Radiology recommends ultrasound as the initial test for suspected gallbladder disease during pregnancy, with 96% accuracy for detecting gallstones 3
• If ultrasound is equivocal and cross-sectional imaging is needed, MRI without contrast is the appropriate next step rather than nuclear medicine studies, as MRI provides excellent diagnostic accuracy without radiation exposure 3

When HIDA Scan May Be Considered

• The American College of Obstetricians and Gynecologists states that nuclear medicine imaging techniques deliver radiation doses much lower than those associated with fetal harm, and if necessary for diagnosis, they should not be withheld from pregnant patients 1, 2, 4
• HIDA scanning may be performed when ultrasound and MRI are inadequate or unavailable and urgent diagnosis of acute cholecystitis is needed, particularly in the second trimester when the risk-benefit ratio is most favorable 3
• The second trimester is the preferred timing for necessary procedures that cannot be deferred, as recommended by the American Gastroenterological Association for biliary interventions 5

Critical Safety Considerations

• Radiation exposure from nuclear medicine studies is typically well below 5 rad (50 mGy), the threshold generally considered safe during pregnancy 1, 2
• A multidisciplinary team including maternal-fetal medicine, gastroenterology, and radiology should be involved in the decision-making process when considering HIDA scan in pregnancy 5
• The clinical indication must be urgent and the potential benefits must justify any theoretical risk to the fetus 1, 2

Alternative Diagnostic Pathway

• For suspected acute cholecystitis with equivocal ultrasound, consider proceeding directly to ERCP if choledocholithiasis or cholangitis is suspected, as ERCP can be both diagnostic and therapeutic during pregnancy 5
• The American Gastroenterological Association recommends ERCP for urgent indications such as choledocholithiasis and cholangitis, ideally performed in the second trimester 5
• If acute cholecystitis is confirmed and surgery is indicated, laparoscopic cholecystectomy is safe during pregnancy and is the standard of care, ideally performed in the second trimester 5

Key Clinical Pitfalls

• Do not assume that all radiation-based imaging is contraindicated in pregnancy—this leads to unnecessary delays in diagnosis and potentially worse maternal and fetal outcomes 1, 2
• Recognize that physiologic changes of pregnancy (such as biliary stasis) increase the risk of gallstone complications, making timely diagnosis essential 5
• Avoid deferring necessary diagnostic procedures beyond the second trimester when possible, as both first and third trimesters carry higher procedural risks 5