Indications for ultrasonography in the first trimester

What are the indications for ultrasonography (US) in the first trimester?

First-trimester US is commonly performed for both symptomatic and asymptomatic pregnant patients for a variety of reasons, including:

  • • Confirmation, dating, and assessing viability of an intrauterine pregnancy, especially when the last menstrual date is uncertain.
  • • Evaluating the etiology of vaginal bleeding, pelvic pain, or a pelvic mass.
  • • Measuring embryonic nuchal translucency (NT) as part of screening for fetal chromosomal abnormalities.
  • • Early screening of certain fetal anomalies (i.e., anencephaly) in high-risk patients.
  • • Imaging guidance for chorionic villus sampling, embryo transfer, and localization and removal of an intrauterine device.

US in the first trimester may be performed transabdominally and/or transvaginally. Transabdominal US provides an overall view of the pelvis and is typically performed first, even without a full urinary bladder. If a normal intrauterine pregnancy is identified transabdominally, transvaginal imaging may be unnecessary. However, if an intrauterine pregnancy or the adnexa are not well visualized transabdominally, transvaginal US should be performed whenever possible. The transvaginal approach uses a higher-frequency transducer that is placed in closer proximity to the uterus and adnexa, allowing for improved resolution and possibly earlier detection of an intrauterine or ectopic pregnancy. Spectral Doppler imaging should be avoided in the first trimester.


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