Ultrasound Prior to Medical Abortion
Ultrasound is not routinely necessary prior to medical abortion when gestational age can be reliably determined by last menstrual period (LMP) and clinical examination, and when there are no risk factors for ectopic pregnancy. 1
When Ultrasound Can Be Omitted
Gestational age determination by LMP and physical examination is sufficient when the patient has a reliable menstrual history and dates are consistent with clinical findings up to 77 days' gestation (11 weeks). 1, 2
Medical abortion can be safely provided without routine ultrasonography in settings where clinicians use reported LMP and physical examination to estimate gestational age, as the mifepristone-misoprostol regimen is highly effective through 63 days' gestation. 2
The absence of controlled trials comparing pre-procedure ultrasound to no ultrasound suggests that routine ultrasound has not been proven to improve safety or efficacy of abortion procedures. 3
When Ultrasound Is Required
Ultrasonography is needed when gestational dating cannot be confirmed using clinical data alone or when there are risk factors for ectopic pregnancy. 1
Ultrasound should be performed when the patient's menstrual history is uncertain, irregular, or unreliable. 1
Risk factors requiring ultrasound evaluation include: previous ectopic pregnancy, current IUD in place, history of pelvic inflammatory disease, or symptoms suggestive of ectopic pregnancy (unilateral pain, abnormal bleeding pattern). 1
Practical Clinical Algorithm
Step 1: Assess gestational age reliability
- If LMP is certain, regular cycles, and dates consistent with examination findings → ultrasound not required. 1, 2
- If LMP uncertain, irregular cycles, or dates inconsistent → perform ultrasound. 1
Step 2: Screen for ectopic pregnancy risk
- No risk factors present → proceed without ultrasound if dating reliable. 1
- Any risk factors present → perform ultrasound to confirm intrauterine location. 1
Step 3: Confirm treatment completion
- Serial quantitative beta-hCG testing is more reliable than ultrasound for confirming successful medical abortion, with hCG dropping to approximately 3% of initial levels being 98.5% reliable. 4
- Ultrasound interpretation of endometrium post-abortion can be difficult due to inhomogeneous structure and is only 89.8% reliable for confirmed intrauterine pregnancies. 4
Common Pitfalls to Avoid
Do not routinely order ultrasound when clinical dating is adequate, as this creates unnecessary barriers to care without proven benefit to safety or efficacy. 3, 2
Avoid relying on transabdominal ultrasound alone if ultrasound is performed, as it underestimates gestational age by an average of 1.6 days and has only 68% sensitivity for detecting an embryonic pole, particularly in patients with higher BMI. 5
Do not use ultrasound as the primary method to confirm abortion completion; clinical history combined with serial hCG testing is more effective. 4