Prenatal diagnosis of Down's Syndrome - Tips from Other Journals

Date: Dec, 1990

The association between major chromosomal abnormalities and maternal age has led to the policy of offering chromosome analysis to pregnant women of advanced maternal age. However, only 25 percent of infants with Down syndrome are born to mothers over 35 years of age. Low levels of maternal serum alpha-fetoprotein have also been related to chromosomal abnormalities. Even if amniocentesis and fetal karyotyping (the two antenatal screening tests currently used to detect Down syndrome) were extended to include all older pregnant women and all women with low serum alpha-fetoprotein levels, fewer than half of all cases of Down syndrome would be detected antenatally. Therefore, prenatal ultrasonographic indicators of Down syndrome have received increasing attention.

Nyberg and colleagues reviewed the prenatal ultrasonograms of 94 consecutive fetuses born with Down syndrome during a six-year period in a hospital in Sweden. The authors found that a variety of findings may be significant. No single abnormality or pattern of abnormalities was found, and ultrasound findings were normal in two-thirds of the cases. Thirty-seven abnormalities were found in 31 fetuses, including two of 11 fetuses assessed by ultrasonography before 14 weeks, 17 of 68 fetuses seen between 14 and 24 weeks and 12 of 15 fetuses seen after 24 weeks. Major anomalies observed on ultrasound examination included cardiac defects (five cases), duodenal atresia (four) and cystic hygromas (four), omphalocoele (two), hydrops fetalis (two) and hydrothorax (one). More subtle abnormalities included nuchal thickening five cases), hyperechogenic bowel (five), mild cerebral ventricular dilatation (three) and growth retardation (six). Four of the cases of nuchal thickening were found late in gestation. Hyperechogenic bowel may be seen in normal fetuses and has also been associated with cystic fibrosis. Neither hyperechogenic bowel nor cerebral ventricular dilatation has previously been associated with Down syndrome. Fetal growth retardation is a well-recognized indicator of chromosomal abnormalities, particularly when it begins early in gestation.

While no single ultrasonographic abnormality was found to be associated with Down syndrome, the authors believe that clinical suspicion should be raised by observation of abnormalities found in the authors' study. Correlation with data from biochemical and chromosomal testing should be sought. (Obstetrics and Gynecology, September 1990, vol. 76, p. 370.)

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