The current role of sonography in the detection of Down's syndrome

Article Abstract:

Down syndrome is a genetic abnormality caused by an abnormal number or configuration of chromosomes. Women over 35 years of age have an increased risk for a Down syndrome fetus. Amniocentesis, a method of prenatal diagnosis for evaluating fetal chromosomes, is recommended for all women over 35. However, less than 20 percent of all Down syndrome fetuses are detected by amniocentesis. Increases in alpha-fetoprotein in the pregnant mother's blood are highly suggestive of chromosomal abnormalities. Although this test would identify 20-30 percent of Down syndrome fetuses, the test also has a high false-positive rate (identifying a fetus as Down syndrome when, in fact, it is not). Ultrasound, the use of high frequency sound to visualize internal structures, can be used to evaluate the anatomy of fetuses. Fetuses with Down syndrome characteristically have short stature and increased thickness in the skin folds of the neck. The biparietal diameter (BPD), an ultrasonographic measurement of the parietal bones of the skull, is used to assess whether the size of the fetus is appropriate for its age. Measurements of the femur bone, the thigh bone, can also be made during ultrasound. A ratio of BPD to femur bone length of less than 0.91 and the presence of a thick skin fold in the neck has been used to diagnose Down syndrome with some degree of success. To validate ultrasonographic parameters used to predict Down syndrome, 22 fetuses were studied. The proportion of fetuses with Down syndrome who had an abnormal test was 36.4 percent. The proportion of normal fetuses with normal tests was 93.4 percent. Assuming that Down syndrome occurs in 1 of 1,000 people in the general population, the proportion of fetuses with an abnormal test was estimated to be 0.6 percent. The sensitivity (identifying fetuses with Down syndrome) of the ultrasound examination was increased from 36.4 percent to 45.5 percent when all three parameters, BPD to femur ratio, skin-fold thickness and measured-to-expected femur length ratio, were used. Larger studies are needed before ultrasonography can be used to detect Down syndrome in fetuses. (Consumer Summary produced by Reliance Medical Information, Inc.)

Usage, Case studies, Ultrasonics in obstetrics

---

The transverse cerebellar diameter in the second trimester is unaffected by Down syndrome

Article Abstract:

The risk that a pregnant woman's fetus has Down syndrome can be calculated according to her age and blood levels of alpha-fetoprotein, a substance whose levels are abnormal in the presence of some types of birth defects. However, risk assessment using these criteria has low sensitivity (rate of true positives) and a high rate of false-positive results (between 4 and 9 percent). As ultrasonographic methods of prenatal diagnosis have improved, it has become possible to perform more detailed fetal evaluation using this approach. The Down syndrome fetus has been reported to have a smaller cerebellum (a part of the brain that helps control balance and coordination) than the normal fetus; since this can be measured with ultrasound, a retrospective study was carried out of 23 second-trimester Down syndrome fetuses. Several measurements were made, including biparietal diameter (a skull measurement), femur (thigh bone) length, head and abdominal circumferences, and transverse cerebellar diameter. The latter value among Down syndrome fetuses was compared with values obtained from 296 normal pregnancies. No difference was found between the transverse cerebellar diameter of Down syndrome fetuses and that of normal fetuses. It is known that the cerebellum in children and adults with Down syndrome weighs less than normal, so the finding that it is not smaller at the second-trimester stage of development implies that the size reduction develops later in maturation. Better ultrasonic methods of detecting abnormalities associated with Down syndrome would be valuable additions to the growing number of available prenatal diagnostic tests. (Consumer Summary produced by Reliance Medical Information, Inc.)

Methods, Physiological aspects, Birth defects, Cerebellum

---

The transverse cerebellar diameter cannot be used to assess gestational age in the small for gestational age fetus

Article Abstract:

Abnormal growth during pregnancy, intrauterine growth retardation (IUGR), is a complication of pregnancy that is associated with a poor fetal outcome. A diagnosis of IUGR is made when the birth weight of the fetus falls in the tenth percentile on standard fetal growth charts. A fetus smaller than 90 percent of the fetuses at the same fetal age is termed small for gestational age (SGA). Methods to differentiate growth-retarded fetuses from normally growing fetuses have proven to be inaccurate. Accurate assessment of gestational age (the age of a fetus) is essential when various fetal parameters are compared. The transverse cerebellar diameter, a measurement of the outer margins of the cerebellum (the part of the brain at the base of the skull), was used to assess gestational age of normal and SGA fetuses. The transverse cerebellar diameter was measured by fetal ultrasonography, the use of high frequency sound to visualize internal structures. Of the 44 SGA fetuses, 29 had a complication of pregnancy indicative of IUGR. The cerebellar diameter was normal in 12 (27.3 percent). In six fetuses (13.6 percent) the measurements were one to two standard deviations below normal, and in 26 fetuses (59.1 percent) the measurements were more than two standard deviations below normal. It is concluded that ultrasonographic measurement of the transverse cerebellar diameter is not useful in assessing the age of SGA fetuses. (Consumer Summary produced by Reliance Medical Information, Inc.)

Testing, Fetal growth retardation, Gestational age

Similar abstracts:

• Abstracts: The role of ultrasonography and amniocentesis in the evaluation of pregnancies at risk for neural tube defects
• Abstracts: Transvaginal ultrasonographic detection of congenital anomalies in the first trimester. Ultrasonographic criteria for the prenatal diagnosis of placental chorionicity in twin gestations
• Abstracts: The efficacy of fiberoptic endoscopic examination and biopsy in the detection of early nasopharyngeal carcinoma
• Abstracts: Fetal biometry as a screening tool for the detection of chromosomally abnormal pregnancies. Sonographically measured nuchal skinfold thickness as a screening tool for Down syndrome: results of a prospective clinical trial
• Abstracts: A controlled study of hand function in nodal and erosive osteoarthritis. Radiographic patterns and associations of osteoarthritis of the knee in patients referred to hospital

This website is not affiliated with document authors or copyright owners. This page is provided for informational purposes only. Unintentional errors are possible.