Is transvaginal ultrasound (TVUS) safe during the 2nd trimester of pregnancy?

Safety of Transvaginal Ultrasound in the Second Trimester of Pregnancy

Transvaginal ultrasound is safe during the second trimester of pregnancy when performed properly by trained professionals. 1

Evidence for Safety

Transvaginal ultrasound (TVUS) has been established as a safe procedure during pregnancy, including the second trimester. The American College of Radiology (ACR) Appropriateness Criteria specifically addresses this issue:

• TVUS has been shown to be both accurate and safe for diagnostic purposes during pregnancy 1
• When performed with real-time imaging as the probe is advanced, TVUS is not contraindicated even in settings such as placenta previa 1
• A prospective study demonstrated that transvaginal ultrasound anomaly scanning conducted in the early second trimester does not cause adverse perinatal outcomes 2

Proper Technique for Safety

For maximum safety, TVUS in the second trimester should be performed with these precautions:

• Real-time imaging should be used throughout the procedure to assess the relationship between the probe tip and the cervix 1
• The angle between the cervix and vaginal probe should be sufficient to prevent inadvertent slippage into the cervix 1
• The procedure should be performed by trained professionals using the "as low as reasonably achievable" principle for acoustic energy 1

Clinical Applications in Second Trimester

TVUS offers several advantages over transabdominal ultrasound (TAS) in the second trimester:

• More complete visualization of the cervix, including the internal os where changes increasing the risk of preterm birth first occur 1
• Higher frequency evaluation and greater detailed assessment due to shorter distance between transducer and target structures 1
• Particularly helpful for cervical-related causes of second and third trimester vaginal bleeding 1

Special Considerations

When to Use Caution

• In cases of premature rupture of membranes, there is limited evidence regarding whether TVUS increases risk of chorioamnionitis 1
• Alternative approaches (transperineal or transrectal) should be considered when TVUS is declined by the patient or deemed too high risk 1

Alternative Approaches

If TVUS is not possible or appropriate:

1. Transperineal ultrasound: A suitable alternative that has shown comparable results to TVUS, especially after 20 weeks' gestation 1
2. Transrectal ultrasound: Useful when transvaginal and transperineal approaches are unsuccessful or declined 1

Benefits vs. Risks

Benefits of TVUS in second trimester:

• Improved detection of cervical shortening, which can lead to interventions reducing preterm birth rates 1
• Better visualization of placental location and potential abnormalities 1
• More accurate assessment in cases of maternal obesity or retroverted uterus 3

Potential risks:

• Ultrasound is a form of energy that demonstrates effects in biological tissues (bioeffects) 4
• These effects can be thermal or mechanical in nature, though diagnostic ultrasound is generally considered safe 4

Conclusion

When performed by trained professionals using proper technique, transvaginal ultrasound is a safe and valuable diagnostic tool during the second trimester of pregnancy. The benefits of accurate diagnosis and potential interventions for conditions like cervical shortening outweigh the theoretical risks.