No. 375-Clinical Practice Guideline on the Use of First Trimester Ultrasound

This guideline reviews the clinical indications for first trimester ultrasound. Proven clinical benefit has been reported from first trimester ultrasound. A Medline search and bibliography reviews in relevant literature provided the evidence. Content and recommendations were 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 Preventive Health Care. 1First 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).2First trimester ultrasound is not recommended to diagnose pregnancy but is recommended to date a pregnancy (ideally at 7–12 weeks). If menstrual dating is reliable and an early comprehensive pregnancy ultrasound (11–14 weeks) is planned, dating should be confirmed concurrently with this exam (III-A).3First trimester ultrasound is recommended prior to pregnancy termination (II-2B).4First trimester ultrasound is recommended during diagnostic or therapeutic procedures requiring visual guidance (e.g., chorionic villus sampling) and prior to prophylactic cervical cerclage placement (I-A).5First trimester ultrasound is recommended for suspected multiple gestation to allow for reliable determination of chorionicity and amnionicity and to establish early fetal genetic and anatomic screening (II-2A).6First trimester ultrasound is recommended in the workup for suspected ectopic pregnancy, molar pregnancy, and suspected pelvic masses (II-1A).7Basic fetal anatomy should be reviewed whenever obstetric ultrasound is done at 11–14 weeks, while women at increased risk of fetal structural and genetic abnormalities can be offered enhanced screening, if performed by ultrasound providers with appropriate imaging expertise (II-3C).8Nuchal translucency screening should be offered as part of a prenatal genetic screening and counselling program by experienced operators with appropriate quality assurance processes in place. Any patient with a nuchal translucency greater than 3.5 should be offered referral to maternal-fetal medicine (II-2A).9When appropriate expertise and resources are in place to screen women for the risk of preeclampsia, first trimester ultrasound is recommended as a valuable component of the screening protocol (I-A).