Is Transvaginal Ultrasound Safe in the First Trimester?
Yes, transvaginal ultrasound (TVS) is completely safe for pregnancy testing and evaluation throughout the first trimester and is, in fact, the single best diagnostic modality for early pregnancy assessment. 1
Primary Recommendation
The American College of Radiology explicitly recommends transvaginal ultrasound as the optimal imaging approach for evaluating early pregnancy in the first trimester, particularly for assessing the endometrium, early pregnancy structures, and adnexa. 1
TVS is routinely used alongside transabdominal ultrasound to accomplish the main goals of first trimester imaging: confirming presence and location of gestational sac(s), determining chorionicity and amnionicity in multiple gestations, providing accurate pregnancy dating, and documenting embryonic cardiac activity. 2
Why TVS is Superior in Early Pregnancy
TVS provides the highest accuracy for critical first trimester assessments because high-resolution transvaginal transducers offer superior visualization of small embryonic structures compared to transabdominal approaches alone. 3
The intertwin membrane in multiple gestations is typically identified by 10 weeks on TVS, and TVS has the highest accuracy for determining chorionicity—correctly assigned in 99.8% of cases (612 of 613 pregnancies). 2
TVS demonstrated additional diagnostic information in 78.3% of normal intrauterine pregnancies compared to transabdominal scanning alone, including better detection of gestational sac, yolk sac, double bleb sign, and embryonic anatomy. 4
Optimal Imaging Protocol
A combined transabdominal and transvaginal approach should be performed when possible, allowing comprehensive evaluation of structures that may be positioned too high for transvaginal visualization alone. 1, 5
The recommended sequence is to begin with transabdominal ultrasound to assess bladder fullness, uterine position, and obtain an overview of the pelvis, followed by transvaginal ultrasound for detailed evaluation of the intrauterine pregnancy, embryonic structures, and adnexa. 1
The bladder should be emptied before transvaginal scanning for optimal visualization. 1
Safety Considerations
Real-time imaging should be used throughout the transvaginal ultrasound procedure. 1
The ALARA principle (as low as reasonably achievable) should be followed regarding acoustic energy, especially at the beginning of gestation. 1
A chaperone should be present for all transvaginal examinations. 1
Clinical Advantages Over Transabdominal Alone
TVS eliminates the need for an uncomfortably full bladder, saving time and allowing potential preoperative patients to remain fasting. 4
TVS is superior in obese patients, patients with retroverted uterus, and bypasses obstacles such as bone, gas-filled bowel, and extensive pelvic adhesions. 4
In abnormal pregnancies, TVS provided more diagnostic information in 64.9% of cases, including detection of embryonic demise, yolk sac, double bleb sign, and subchorionic hemorrhage. 4
When TVS is Particularly Indicated
TVS should be performed when transabdominal evaluation is considered incomplete or suboptimal, which is common in early first trimester when the pregnancy is still relatively small. 2, 1
TVS is essential when an intertwin membrane is not seen transabdominally in multiple gestations, as it can be attempted because of superior resolution. 2
For patients with previous cesarean delivery or uterine instrumentation, TVS assessment for placenta accreta spectrum can be performed. 2
Common Pitfalls to Avoid
Do not rely solely on transabdominal ultrasound in the first trimester, as resolution may be inadequate for complete assessment of early pregnancy structures, particularly at 8.5 weeks gestation or earlier. 1
Do not mistake the limited maneuverability of the TVS probe or the unorthodox position and angle of the transducer as contraindications—these are technical considerations that become easier with experience, not safety concerns. 4