ATLANTA -- An isolated, subtle anomaly seen on a midtrimester ultrasound may be innocuous if the mother is not at high risk and the triple screen is normal.
But with advanced maternal age or if multiple abnormalities are present, an adverse outcome is possible and further diagnostic procedures are warranted, Dr. Ray O. Bahado-Singh said at a conference on high-risk obstetrics sponsored by Symposia Medicus.
A single umbilical artery, for example, has been reported to be associated with a whole range of gross anomalies, particularly cardiovascular, in 21%-76% of cases. Should this be seen on a screening ultrasound, therefore, a targeted ultrasound should be done to rule out a structural abnormality. A thorough heart examination also must be performed, and possibly a fetal echocardiogram, said Dr. Bahado-Singh, director of maternal-fetal medicine at the University of Cincinnati.
Karyotyping should be done if other anomalies are present. "And even if there are no structural abnormalities, it is not inappropriate to do a repeat ultrasound at 32-34 weeks, because there is a sense from the literature that a single umbilical artery is associated with fetal growth restriction."
Another perplexing ultrasound finding is that of an isolated choroid plexus cyst. Whether the presence of this anomaly increases the risk for aneuploidy--and whether karyotyping should be done--remains controversial.
"Obviously, in the presence of an associated structural defect, karyotyping is indicated," Dr. Bahado-Singh said. Otherwise, a targeted ultrasound and triple screen should provide sufficient information to determine whether invasive testing is needed. In the vast majority of cases, the cyst will resolve by about 24 weeks, he said.
A third subtle anomaly is an intracardiac echogenic focus, which has been reported in association with trisomy 13 in 39% of cases and with trisomy 21 in 16% of cases. With this finding, advanced maternal age and location of the focus are significant. "Most commonly this is seen in the left ventricle. If found in the right ventricle or, particularly, if it is bilateral, the risk is substantially higher," he said.
If the patient is younger than 35 and has no other markers, a triple screen may suffice. But if she is older than 35 and has other soft markers or the triple screen is positive, amniocentesis is recommended.
A further subtle anomaly that has been linked to chromosomal defects and developmental delays is mild (11-14 mm) ventriculomegaly. If this condition resolves or remains stable in utero, normal postnatal development can be expected in 78% and 56% of cases, respectively, some studies suggest. But if it progresses, the percentage likely to develop normally drops to 24%, he said.
A targeted ultrasound should be done when mild ventriculomegaly is present, along with a prenatal work-up to look for triggers such as viral infection. A fetal MRI should be considered, because some evidence exists that this may be more, discriminatory for subtle but significant intracranial anomalies, such as neuronal migrational disorders, than ultrasound, he said.
COPYRIGHT 2003 International Medical News Group
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