Ultrasonographic screening for the Down syndrome fetus Charles J. Lockwood, MD, Lauren Lynch, MD, and Richard L. Berkowitz, MD New York, New York The usefulness of ultrasonography in detecting fetuses with Down syndrome iii the second trimester has been the subject of considerable debate during the past 3 years. Conflicting reports have led to increasing confusion about the subject in the medical community and among the public. A review of the existing literature indicates that structural malformations that are chiefly cardiac are present in half of Down syndrome fetuses but are not consistently found during routine second· trimester ultrasonography. Although excess posterior nuchal skin-fold thickness is frequently present in infants with Down syndrome, it is also nOt consistently identified during second-trimester ultrasonographic examinations. Studies evaluating the efficacy of screening programs that are based on femur length shortening associated with Down syndrome have revealed markedly discrepant intercenter results. Although variations in methods may account for some of the observed variability, the magnitude of femoral shortening in Down syndrome suggests that this measurement may be only marginally useful. In summary, antenatal ultrasonography will allow for the detection of only those fetuses with Down syndrome who have multiple characteristic phenotypic features or anomalies. Moreover, current second-trimester ultrasonography does not appear to be either sensitive enough or specific enough to be used as a unique Down syndrome screening modality; however, it may be a useful adjunct to maternal age and serum biochemical markers in the assignment of risk for Down syndrome. (AM J OasTET GVNECOL 1991 ;165:349-52.)

Key words: Ultrasonography, Down syndrome, screening The incidence of Down syndrome is approximately in 1000 live births.' This incidence is expected to increase modestly over the next 10 years as the number of women between 35 and 49 years of age increases! However, the infants of women older than 34 will still account for only 8.6% of all live births and 39% of Down syndrome cases by the year 2000. Thus even a fully used Down syndrome screening program that is based on maternal age will fail to identify 61 % of Down syndrome cases." The association of decreased maternal serum o:-fetoprotein levels with fetal Down syndrome has now been well established. Risk determination that is based on a combination of maternal serum o:-fetoprotein value and maternal age allows the detection of up to onethird of fetuses with Down syndrome and necessitates karyotype analysis in 5% of pregnant patients younger than 35. 3 However, Down syndrome risk assignment paradigms that use maternal age with a combination of maternal serum o:-fetoprotein, human chorionic gonadotropin, and estriol values may identify 60% of fetuses with Down syndrome and necessitate karyotype analysis in only 5% of pregnant women! From the Department of Obstetrics, Gynecology and Reproductive Sciences, Mount Sinai School of Medicine. Dr. Lockwood is a recipient of an American Association of Obstetricians and Gynecologists Foundation Kennedy-Dannreuther Fellowship. Reprint requests: Chades j. Lockwood MD, Department of Obstetrics, Gynecology and Reproductive Sciences, Mount Sinai School of Medicine, One Gustave L. Levy Place, New York, NY 10029-6574. 6 11126200

As a result of the explosive increase in the number of women who are undergoing diagnostic antenatal ultrasonographic studies, it was logical that ultrasonography also be evaluated in the quest for improved detection rates of Down syndrome. Unfortunately, initial reports have provided contradictory results and inconsistent methodologic approaches. An examination of the published experience of those who have used ultrasonographic indicators to detect fetuses with Down syndrome and speculations about the usefulness of this approach are the subjects of this review.

Why screen for fetal Down syndrome with ultrasonography? Because most pregnant women now routinely undergo ultrasonographic evaluation in the second trimester, failure to use ultrasonographic information that could alter risk assignment of Down syndrome at the time of those examinations would be injudicious. However, this argument for the use of ultrasonographically derived data to determine the risk of Down syndrome requires that such data be reliably obtained, be effective in discriminating between fetuses with Down syndrome and unaffected fetuses, and be obtainable at a gestational age that is early enough to be useful clinically. Ultrasonographic detection of Down syndrome fetus: Identification of coexistent anomalies Certain malformations have been specifically associated with fetal Down syndrome. For example, 30% of 349

350

Lockwood, Lynch, and Berkowitz

fetuses with duodenal atresia have Down syndrome,' but only 3% to 8% of fetuses with Down syndrome have detectable upper gastrointestinal tract obstructions. Moreover, although the ultrasonographic diagnosis of duodenal atresia is readily made after 28 weeks' gestation, its consistent diagnosis may be difficult or impossible before 24 weeks.' Thus duodenal atresia, which is suggestive of Down syndrome, is not a useful ultrasonographic marker for most cases of Down syndrome. The prevalence of aneuploidy in fetuses diagnosed with congenital heart defects has been reported to be 32%.6 However, the vast m

Ultrasonographic screening for the Down syndrome fetus.

The usefulness of ultrasonography in detecting fetuses with Down syndrome in the second trimester has been the subject of considerable debate during t...
510KB Sizes 0 Downloads 0 Views