The use of first trimester ultrasound.

OBJECTIVE To review the clinical indications for first trimester ultrasound. OUTCOME Proven clinical benefit from first trimester ultrasound. EVIDENCE MEDLINE search and bibliography reviews in relevant literature. VALUES Content and recommendations reviewed by the principal authors and the Diagnostic Imaging Committee of the Society of Obstetricians and Gynaecologists of Canada. Levels of evidence were judged as outlined by the Canadian Task Force on the Periodic Health Examination. RECOMMENDATIONS 1. First trimester ultrasound is recommended for assessment of threatened abortion to document fetal viability (II-2B) or for incomplete abortion to identify retained products of conception (II-2B). 2. First trimester ultrasound is not recommended to diagnose pregnancy, to date pregnancy when last normal menstrual period and physical examination are concordant, or to investigate an inevitable abortion (II-2B). First trimester ultrasound is indicated when last menstrual period date is uncertain (I-A). 3. First trimester ultrasound is recommended prior to pregnancy termination. (II-2B) 4. First trimester ultrasound is recommended during diagnostic or therapeutic procedures requiring visual guidance (e.g., chorionic villus sampling, amniocentesis) and prior to cervical cerclage placement. (I-A) 5. First trimester ultrasound is recommended for suspected multiple gestation to allow for reliable determination of chorionicity or amnionicity. (II-2A) 6. First trimester ultrasound is recommended for suspected ectopic pregnancy, molar pregnancy, and suspected pelvic masses. (II-1A) 7. First trimester ultrasound is recommended for early assessment of anatomic development in situations of increased risk for major fetal congenital malformations. (II-3C) 8. Nuchal translucency screening should only be offered as part of a comprehensive prenatal screening and counselling program by experienced operators with appropriate quality assurance processes in place (II-2A).