Fetal Soft Markers in Obstetric Ultrasound
162 - Published June 2005
Objective: To evaluate ultrasound “soft markers” used in fetal genetic
Options: Ultrasound screening at 16 to 20 weeks is one of the most
common genetic screening and (or) diagnostic tests used during
pregnancy. The practical concern for ultrasound screening is
false-positive and false-negative (missed or not present) results.
The use and understanding of ultrasound soft markers and their
screening relative risks is an important option in the care of
pregnant women. Currently, the presence of a “significant”
ultrasound marker adds risk to the likelihood of fetal pathology, but
the absence of soft markers, except in controlled situations, should
not be used to reduce fetal risk.
Outcomes: The use of ultrasound in pregnancy has significant health
and economic outcomes for families and the health care system,
compared with no ultrasound use. The Society of Obstetricians and
Gynaecologists of Canada (SOGC) recommends a single “routine”
ultrasound evaluation at 16 to 20 weeks in all pregnancies.
Patients need to be counselled about the positive and negative
findings that ultrasound may reveal so they are prepared for
unexpected pregnancy knowledge and the possibility of further
testing options being offered.
Evidence: Committee members were asked to review specific soft
marker ultrasound topics after consensus was reached on the
most commonly published soft markers. Medline and PubMed
databases were searched for peer-reviewed English articles
published from 1985 to 2003. Reviews of each soft marker topic
were written by committee members with quality of evidence and
classification of recommendations. These reviews were then
circulated and discussed by the combined committee. Final format
for the guideline was completed by the committee chairpersons.
Values: The quality of evidence and classification of
recommendations followed discussion and consensus by the
combined committees of Diagnostic Imaging and Genetics of the
Benefits, Harms, Costs: It is not possible at this time to determine
the benefits, harms, and costs of the guideline because this would
require health surveillance and research and health resources not
presently available; however, these factors need to be evaluated in
a prospective approach by provincial and tertiary initiatives.
Consideration of these issues is in the options and outcome
section of this abstract.
1. The screening ultrasound at 16 to 20 weeks should evaluate 8
markers, 5 of which (thickened nuchal fold, echogenic bowel, mild
ventriculomegaly, echogenic focus in the heart, and choroid plexus
cyst) are associated with an increased risk of fetal aneuploidy, and
in some cases with nonchromosomal problems, while 3 (single
umbilical artery, enlarged cisterna magna, and pyelectasis) are
only associated with an increased risk of nonchromosomal
abnormalities when seen in isolation (II-2 B).
2. Identification of soft markers for fetal aneuploidy requires
correlation with other risk factors, including history, maternal age,
and maternal serum testing results (II-1 A).
3. Soft markers identify a significant increase in fetal risk for genetic
disease. Timely referral for confirmation, counselling, and
investigation is required to maximize management options (III-B).
Validation: Peer-reviewed guideline development is part of the
committee process in addition to SOGC council and editorial
J Obstet Gynaecol Can 2005;27(6):592–612