Fetal biometry as a screening tool for the detection of chromosomally abnormal pregnancies

Article Abstract:

It is a standard of practice to perform amniocentesis, an invasive method of prenatal diagnosis in which a sample of amniotic fluid is taken from inside the membrane surrounding the fetus, on all pregnancies in women over 35. Although it is known that the risk of having a chromosomally defective fetus increases with age, over 80 percent of chromosomally abnormal fetuses are born to women under 35. Since amniocentesis is not performed on all pregnancies, a noninvasive method of detecting fetuses with chromosomal abnormalities is needed for younger women. Some prenatal blood tests performed on pregnant mothers blood can detect biochemical markers that are highly suggestive of fetal abnormalities. In addition, ultrasonography, the use of high frequency sound to visualize internal structures, can be used recognize malformations characteristic of certain chromosomal defects. Fetuses with Down's syndrome, an abnormal number of chromosomes, typically have short stature and increased skin fold thickness in the neck region. The ultrasonographic evaluations of biparietal diameter (BPD, a measurement of both the parietal bones in the skull) and length of the large leg bone (femur) have not been proven to be able to detect Down's syndrome. To see if ultrasonographic evaluations is useful in diagnosing chromosomally abnormal fetuses, 48 fetuses with confirmed genetic abnormalities were assessed. The BPD/femur ratio correctly detected 18 percent of the fetuses with Down's syndrome, and falsely identified four percent. The tool was able to positively predict Down's syndrome in one of 169 fetuses. When other chromosomal abnormalities were included (trisomy 21, 18 and 13), the sensitivity of the test increased to one in 78 (29 percent sensitivity rate). The femur length was less useful in predicting chromosomally abnormal fetuses. Although the value of biometry in detecting chromosomal abnormalities is promising, verification is needed. (Consumer Summary produced by Reliance Medical Information, Inc.)

Usage, Abnormalities, Genetic screening, Genetic testing

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Sonographically measured nuchal skinfold thickness as a screening tool for Down syndrome: results of a prospective clinical trial

Article Abstract:

Down syndrome is a genetic disorder affecting newborns. It is more likely to occur in children born to women age 35 or older than in children born to younger women. Amniocentesis, a diagnostic test whereby fluid is drawn from the fetal sac and analyzed for evidence of genetic defects, is often performed on older women who are pregnant. The procedure is invasive and thus poses some risks, so it is not generally performed on younger pregnant women. Even though the risk for fetal genetic defects is much lower in younger women, 80 percent of all fetuses born with these defects are delivered by women under the age of 35 because the birth rate is much higher for them. For younger women, an inexpensive, noninvasive diagnostic technique for examining the fetus for genetic defects would be desirable. This study examined the value of sonography, an imaging technique that uses high-frequency sound waves, to detect Down syndrome in fetuses by measuring nuchal (back of neck) skinfold thickness. A recent study reported that when the nuchal thickness in a fetus was greater than 6 mm, Down syndrome was likely. Sonography was performed on 3,338 consecutive pregnancies and nuchal skinfold measurements of the fetuses were made. Results showed that 47 (1.4 percent) of the fetuses had skinfold thicknesses of 6 mm or greater. Twelve of the 47 (26 percent) were eventually found to have Down syndrome. A total of 16 fetuses were eventually found to suffer from Down syndrome, so the sensitivity of this test was 75 percent (12 of 16). These results indicate that sonography scanning to measure nuchal skinfold in fetuses is a valid predictor of Down syndrome and that amniocentesis should be performed when a skinfold thickness of 6 mm or greater is found. (Consumer Summary produced by Reliance Medical Information, Inc.)

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Congenital hydronephrosis: correlation of fetal ultrasonographic findings with infant outcome

Article Abstract:

Congenital hydronephrosis is a common birth defect characterized by the blockage of urine flow, resulting in the collection of urine in the kidney. This leads to the formation of a cyst, or sac-like structure, and the distention and wasting away of the kidney. This birth-related disorder affects 1 in 330 infants and is associated with the presence of a mass in the abdomen, periodic pain, vomiting, failure to thrive, and infection of the urinary tract. If the defect is corrected within the first 6 to 12 months after birth, the patient will have a good outcome. If untreated, congenital hydronephrosis may lead to impaired kidney function. However, less than 25 percent of cases are detected before age one year, and only 55 percent are detected by the age of five years. Congenital hydronephrosis may be diagnosed before birth by ultrasonography, the use of sound waves to visualize tissue. The criteria used to diagnose congenital hydronephrosis by ultrasonography were assessed in 63 fetuses with suspected hydronephrosis. Various measurements of the kidney and renal pelvis (the portion of the kidney attached to the ureters, which connect the kidney to the bladder) were performed by ultrasonography. A diagnosis of hydronephrosis was confirmed after birth in 45 fetuses, including 31 with abnormal kidney function and/or need for surgical repair. Fourteen infants had normal kidney function and did not need surgery. Comparison of ultrasonography findings before birth with the diagnosis after birth showed that the ultrasonographically measured anteroposterior diameter of the renal pelvis was the most sensitive indicator of congenital hydronephrosis in the fetus. (Consumer Summary produced by Reliance Medical Information, Inc.)

Ultrasound imaging, Birth defects, Hydronephrosis

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