Fetal Soft Markers in Obstetric Ultrasound


1. EICF should be evaluated as part of the 4-chamber cardiac review during the 16- to 20- week ultrasound.
2. Isolated EICF with a fetal aneuploidy risk less than 1/600 by maternal age (31 years) or maternal serum screen requires no further investigations.
3. Women with an isolated EICF and a fetal aneuploidy risk greater than 1/600 by maternal age (31 years) or maternal serum screening should be offered counselling regarding fetal karyotyping.
4. Women with right-sided, biventricular, multiple, particularly conspicuous, or nonisolated EICF should be offered referral for expert review and possible karyotyping.


1. Evaluation of fetal kidneys is a part of the screening ultrasound at 16 to 20 weeks,’ and if pyelectasis is visualized, the renal pelvis should be measured in the anterior/posterior diameter.
2. All fetuses with renal pelvic measurements 5 mm should have a neonatal ultrasound, and those having measurements > 10 mm should be considered for a third trimester scan.
3. Isolated mild pyelectasis does not require fetal karyotyping.
4. Referral for pyelectasis should be considered with additional ultrasound findings and (or) in women at increased risk for fetal aneuploidy owing to maternal age or maternal serum screen results.


1. Assessment of cord vessels is considered a part of the routine obstetric ultrasound at 16 to 20 weeks.
2. The finding of a single umbilical artery requires a more detailed review of fetal anatomy, including kidneys and heart (fetal echo).
3. An isolated single umbilical artery does not warrant invasive testing for fetal aneuploidy.


1. Evaluation of the fetal bowel should be done routinely during the 16- to 20-week obstetric ultrasound.
2. Echogenic bowel should be identified by comparison with the echogenicity of surrounding bone using an appropriate transducer and gain setting. Bowel echogenicity equal to or greater than bone is significant (grade 2 or 3).
3. No further investigations are required for grade 1 echogenic bowel.
4. Grade 2 and 3 echogenic bowel is associated with both chromosomal and nonchromosomal abnormalities. Expert review is recommended to initiate the following: a. detailed ultrasound evaluation looking for additional structural anomalies or other soft markers of aneuploidy b. detailed evaluation of the fetal abdomen looking for signs of bowel obstruction or perforation (II-2 B); and c. detailed evaluation of placental characteristics (echogenicity, thickness, position, and placental cord insertion site) (II-2 B); d. genetic counselling (II-2 A); e. laboratory investigations that
should be offered, including fetal karyotype, maternal serum screening, DNA testing for cystic fibrosis (if appropriate), and testing for congenital infection.


1. Nuchal fold measurement should be a part of the screening obstetric ultrasound at 16 to 20 weeks.
2. A thickened nuchal fold significantly increases the risk of fetal aneuploidy. Expert review is recommended, and karyotyping should be offered.
3. A thickened nuchal fold is associated with congenital heart disease and rarely with other genetic syndromes. Expert review is recommended.


1. Fetal cerebral ventricles should be measured if they subjectively appear larger than the choroid plexus.
2. Cerebral ventricles greater than or equal to 10 mm are associated with chromosomal and central nervous system pathology. Expert review should be initiated to obtain the following: a. a detailed anatomic evaluation looking for additional malformations or soft markers; b. laboratory investigation for the presence of congenital infection or fetal aneuploidy; and c. MRI as a potential additional imaging technique.
3. Neonatal assessment and follow-up are important to rule out associated abnormalities and are important because of the potential for subsequent abnormal neurodevelopment.


1. Choroid plexus should be evaluated for the presence of discrete cysts during the 16- to 20-week ultrasound.
2. Isolated CPCs require no further investigation when maternal age or the serum screen equivalent is less than the risk of a 35-year-old.
3. Fetal karyotyping should only be offered if isolated CPCs are found in women 35 years or older or if the maternal serum screen is positive for either trisomy 18 or 21.
4. All women with fetal CPCs and additional malformation should be offered referral and karyotyping.
5. All women with CPCs and additional soft markers should be offered additional counselling and further ultrasound review.


1. Review of the fetal cerebellum and cisterna magna is a routine part of the screening ultrasound at 16 to 20 weeks. If the cisterna magna is subjectively increased, a measurement should be taken.
2. An isolated enlarged cisterna magna is not an indication for fetal karyotyping.
3. With an enlarged cisterna magna, expert review is recommended for follow-up ultrasounds and possible other imaging modalities (for example, MRI) and investigations.
4. If the enlarged cisterna magna is seen in association with other abnormal findings, fetal karyotyping should be offered.


1. Although femur length is standard biometry on the 16- to 20-week ultrasound, the assessment for relative shortness is not part of the screening evaluation.
2. Relative femur shortening is an ultrasound marker for trisomy 21 and should be considered during tertiary level evaluation.
3. If a femur appears abnormal or measures short on screening ultrasound, other long bones should be assessed and referral with follow-up ultrasound considered.


1. Humeral length is not part of the current screening ultrasound at 16 to 20 weeks but should be considered for future inclusion.
2. Relative humeral shortening is an ultrasound marker for trisomy 21 and should be considered during tertiary level evaluation.
3. If the humerus is evaluated and appears abnormal or short, other long bones should be assessed and referral with follow-up ultrasound considered.


1. Assessment of the fetal nasal bone is not considered a part of the screening ultrasound at 16 to 20 weeks.
2. Hypoplastic or absence nasal bone is an ultrasound marker for fetal Down syndrome, and if suspected, expert review is recommended.


1. Imaging of the outstretched hand to evaluate for fifth finger clinodactyly is not an expectation during the 16- to 20-week ultrasound.
2. Fifth finger clinodactyly is associated with trisomy 21 and should be considered for research or tertiary-level evaluation.

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