Robert G. Resta

Humerus and femur length shortening in the detection of Down's syndrome

OBJECTIVE Our purpose was to determine the utility of screening for humerus and femur length shortening in prenatal detection of Downs syndrome (trisomy 21). STUDY DESIGN On the basis of the biparietal diameter, predicted humerus and femur lengths were derived from a sample control group of 350 karyotypically normal fetuses. The regression formulas were prospectively applied to 45 consecutive fetuses with Downs syndrome and 942 fetuses with normal karyotypes. Ratios of measured humerus length/predicted humerus length and measured femur length/predicted femur length were calculated for each fetus. RESULTS Eleven of 45 (24.4%) fetuses with Downs syndrome had short humerus (measured humerus length/predicted humerus length ratio of < or = 0.89), and 11 (24.4%) had short femur (measured femur length/predicted femur length ratio of < or = 0.91. In comparison, among 942 karyotypically normal fetuses only 43 (4.5%) showed short humerus and 44 (4.7%) showed short femur (p < 0.05). Fetuses with both short humerus and short femur carried an 11-fold greater risk of Downs syndrome (risk ratio = 11.1; 95% confidence interval = 5.0 to 25.0). CONCLUSION Prenatal ultrasonographic detection of short humerus to short femur, or both significantly increase the risk of Downs syndrome; this information may be useful in screening programs.

Prenatal sonographic findings of trisomy 18: review of 47 cases.

Prenatal sonographic findings were reviewed in 47 consecutive fetuses with trisomy 18. One or more abnormalities, excluding choroid plexus cysts, were found in 39 fetuses (83%), including 21 of 29 (72%) fetuses examined between 14 and 24 weeks and all 18 (100%) fetuses examined after 24 weeks. Abnormalities most frequently detected before 24 weeks included cystic hygromas, nuchal thickening, and meningomyelocele. Intrauterine growth retardation, cardiac defects, and an enlarged cisterna magna were detected more frequently after 24 weeks than before 24 weeks (P < 0.05). Intrauterine growth retardation was the single most common abnormality, detected in 51% of all fetuses and 89% of fetuses examined after 24 weeks. Choroid plexus cysts were identified in 25% (12 of 47) of fetuses, including 11 of 29 (38%) fetuses seen before 24 weeks. Additional abnormalities were identified in 10 of 12 (83%) fetuses with choroid plexus cysts; one of the two remaining fetuses showed clenched hands and a cardiac anomaly at autopsy, and the other showed unusually large, multiple choroid plexus cysts. Awareness of the type of anomalies and the usual menstrual age of diagnosis in fetuses with trisomy 18 should improve patient counseling and prenatal detection of fetuses considered at risk for this disorder.

Role of prenatal ultrasonography in women with positive screen for Down syndrome on the basis of maternal serum markers

OBJECTIVE Our purpose was to evaluate the usefulness of prenatal ultrasonography among women with a positive screen for fetal Down syndrome on the basis of three biochemical markers--maternal serum alpha-fetoprotein, human chorionic gonadotropin, and unconjugated estriol. STUDY DESIGN A total of 395 women underwent prenatal ultrasonography at a single institution after being identified as screen positive (midtrimester risk > or = 1:195) on the basis of triple-marker screening between 15 and 18 weeks. Ultrasonographic findings were compared with the biochemical markers and the eventual fetal outcome for these patients. Ultrasonographic abnormalities that were evaluated included structural defects, nuchal thickening or cystic hygroma, echogenic bowel, cerebral ventricular dilatation, pyelectasis, and shortened femur. RESULTS Among 395 patients, 374 (94.7%) had normal karyotype by genetic amniocentesis (n = 232) or postnatal follow-up (n = 142), 18 (4.5%) proved to have Down syndrome, and three had other karyotypic abnormalities. One or more ultrasonographic abnormalities were found in nine of 18 (50%) with Down syndrome compared to 27 of 377 (7.2%) other fetuses (p < 0.001). Fetuses with abnormal ultrasonography results included three with other chromosome abnormalities and five with nonchromosomal anomalies. An abnormal ultrasonography result increased the risk of Down syndrome by 5.6-fold (25% from 4.5%) and a negative result reduced the risk by 45% (2.5% from 4.5%). The value of ultrasonography is further enhanced when all chromosome abnormalities and nonchromosomal anomalies are considered. CONCLUSION Abnormal ultrasonographic findings increase the risk for Down syndrome, whereas normal findings are less predictive of normalcy. After correction for inaccurate menstrual dates, genetic amniocentesis should be offered in spite of a normal ultrasonography result among women with positive triple screen.

Femur length shortening in the detection of Down syndrome:Is prenatal screening feasible?

The potential utility of screening for femur length shortening in prenatal detection of Down syndrome (trisomy 21) was evaluated by comparing 49 consecutive fetuses with Down syndrome with 572 chromosomally normal fetuses before genetic amniocentesis. Ratios of measured femur length/predicted femur length and biparietal diameter/femur length were calculated for each fetus. The predicted femur length was calculated from a regression equation relating the biparietal diameter and femur length derived from a sample control group. With this normal regression equation, 7 of 49 (14.3%) fetuses with Down syndrome had short femur lengths (measured femur length/predicted femur length ratio of less than or equal to 0.91) compared with 35 of 572 (6.1%) fetuses with a normal karyotype (p less than 0.05). However, the maximum positive predictive value for identification of Down syndrome based on short femur lengths was only 0.93% for a high-risk population (prevalence of Down syndrome, 1:250) and 0.33% for a low-risk population (prevalence of Down syndrome, 1:700). We conclude that ultrasonographic screening of short femur length is less effective for prenatal detection of Down syndrome than initially suggested.

Prenatal sonographic findings of Down syndrome: Review of 94 cases

Prenatal ultrasound findings were reviewed in 94 consecutive fetuses with proved Down syndrome (trisomy 21) during a 6-year period at a single institution. One or more abnormalities were found in 31 fetuses (33%), including two of 11 fetuses seen before 14 weeks, 17 of 68 fetuses seen between 14-24 weeks, and 12 of 15 fetuses seen after 24 weeks. Major anomalies detected included cardiac defects (five), duodenal atresia (four), cystic hygromas (four), omphalocele (two), hydrops (two), and hydrothorax (one). Nuchal thickening was observed in five fetuses, including four of 25 second-trimester fetuses evaluated prospectively during the last 2 years of the study. Mild cerebral ventricular dilatation (three) and hyperechogenic bowel (five) are new findings that have not been generally associated with Down syndrome. A variety of prenatal sonographic abnormalities may be associated with Down syndrome, and the frequency of detecting most abnormalities increases with menstrual age. Anomalies more frequently detected before 20 weeks include cystic hygromas, nuchal thickening, and hyperechogenic bowel. Awareness of the sonographic findings associated with Down syndrome should result in improved detection of this disorder.