Please note: In 2003, the CTF updated its Grades of Recommendations to include an "I Recommendation" for situations where insufficient evidence exists to allow a recommendation to be made.  (Formerly, these situations were captured under a "C Recommendation".)  This change is not retroactive, and all "C Recommendations" made prior to 2003 have not been reevaluated in light of the new "I" recommendation grade.  For a discussion of these recommendation grades, please link to the 2003 article in the Canadian Medical Association Journal here.

Routine Prenatal Ultrasound Screening

Objective
To make recommendations for the use of a single or serial ultrasound examination to estimate gestational age and to detect multiple pregnancies, malformation or intrauterine growth retardation in pregnant Canadian women.

Burden of Suffering
The goal of prenatal ultrasound screening is to reduce the rates of perinatal illness and death from several causes, some of which (e.g. IUGR) are etiologically non-specific.  Therefore, the Task Force has reviewed the evidence on the impact of prenatal ultrasound screening on measures of perinatal illness and death rather than on its ability to detect specific abnormalities.

Options
A single ultrasound examination in the second trimester of pregnancy or serial (usually 2) ultrasound examinations, 1 in the second trimester and 1 in the third trimester.

Outcomes
Perinatal mortality and illness, Apgar scores, decreased rates of induced labour (better estimates of gestational age), earlier detection of twin pregnancies, increased birth weight, and increased rates of therapeutic abortions because of identification of fetal abnormalities.

Evidence
MEDLINE was searched up to October 1993 using the keywords ultrasonography and randomized controlled trial. Bibliographies of retrieved articles were also searched. Inclusion criteria were random allocation of pregnant women to routine ultrasonography or no routine ultrasonography and outcomes of perinatal illness or death were provided. The Cochrane Database of Systematic Reviews was also searched.

Values
The 13-member Task Force of experts in family medicine, geriatric medicine, pediatrics, psychiatry and epidemiology used an evidence-based method for evaluating the effectiveness of preventive health care interventions. Recommendations were not based on cost-effectiveness of options. Patient preferences were not discussed.

Background papers providing critical appraisal of the evidence and tentative recommendations prepared by the chapter author were pre-circulated to the members. Evidence for this topic was presented and deliberated upon in 1- to 2-day meetings from October 1993 to March 1994. Consensus was reached on final recommendations.

Benefits, Harms, and Costs
4 RCTs of single ultrasound examinations were examined. 3 showed no difference in fetal mortality whereas the fourth one did although this difference was no longer significant when the increased number of therapeutic abortions for malformations were considered as deaths. The 4 studies did not differ for Apgar scores or days in the special care nursery. 1 study showed that women who had ultrasound examination had fewer inductions and a slight increase in birth weight (42 g, P = 0.008), and another showed earlier detection of twin pregnancies (100% detected before 21 weeks in the study group vs 76% in the control group).

The 4 studies that assessed multiple ultrasound examinations showed no differences in Apgar scores and perinatal deaths. 1 study showed fewer hospital days and 1 showed more hospital days with ultrasonography.

Systematic reviews showed that a single ultrasound examination was associated with early detection of twin pregnancies, decreased rates of induction, increased birth weight in singleton pregnancies, increased rates of therapeutic abortions because of fetal abnormalities and no differences in perinatal mortality or Apgar scores. Late ultrasound examination showed no differences for mortality, morbidity, or induction of labour. 1 meta-analysis showed decreased perinatal mortality with a single ultrasound examination.

Recommendations
Recommendation grade [A, B, C, D, E]  and level of evidence [I, II-1, II-2, II-3, III] are indicated after each recommendation. Citations in support of individual recommendations are identified in the guideline text.

• There is fair evidence to include a single ultrasound examination in the second trimester of pregnancy in women without clinical indications (normal pregnancy) [B, I].
• There is insufficient evidence to include or exclude serial ultrasound examinations in the second and third trimester of pregnancy in women without clinical indications (normal pregnancy) [C, I].

Sponsors
The Canadian Task Force on Preventive Health Care developed this guideline with funding from Health Canada.

Source Document
Anderson G.  Routine prenatal ultrasound screening. In: Canadian Task Force on the Periodic Health Examination. Canadian Guide to Clinical Preventive Health Care. Ottawa: Health Canada, 1994; 4-14.