Ultrasound Screening for Fetal Down Syndrome in the Second Trimester of Pregnancy / 대한산부인과학회잡지

OBJECTIVE: To determine the risk of Down syndrome in fetuses with sonographic markers using the likelihood ratios and individual risk assessment. METHODS: We retrospectively evaluated the midtrimester genetic sonographic features of fetuses with Down syndrome and compared them with euploid fetuses. Patients were referred for an increased risk of aneuploidy and evaluated for the presence of structural defects, a nuchal fold, short long bones, pyelectasis, brachycephaly, small stomach, and hyperechoic bowel. Outcome information included the results of genetic amniocentesis (if performed), the results of pediatric assessment, and follow-up after birth. The sensitivity, specificity, and likelihood ratios for markers ware calculated isolated findings. RESULTS: There were 59 fetuses with Down syndrome and 600 euploid fetuses. The presence of any marker resulted in sensitivity for the detection of Down syndrome of 86.4% with a false-positive rate of 13.6%. Structural defect had a likelihood ratio of 77.8. As an isolated marker, the nuchal fold, short humerus, short femur, echogenic bowel and renal pyelectasia has a likelihood ratio of 20.2, 12.7, 3.9, 2.5, 1.1 respectively. Other isolated markers had low likelihood ratios because of the higher prevalence in the unaffected population. CONCLUSION: Combining second-trimester serum testing and fetal sonography is a feasible approach to Down syndrome screening, compatible with current obstetric practice. Although an isolated marker with a low likelihood ratio may not increase a patient's risk of Down syndrome, the presence of such a marker precludes reducing the risk of aneuploidy. This information will be useful in counseling pregnant women who are at high risk for fetal Down syndrome and who prefer to undergo genetic sonography before deciding about genetic amniocentesis.

Ultrasound Screening for Fetal Down Syndrome in the Second Trimester of Pregnancy / 대한산부인과학회잡지

OBJECTIVE: To determine the risk of Down syndrome in fetuses with sonographic markers using the likelihood ratios and individual risk assessment. METHODS: We retrospectively evaluated the midtrimester genetic sonographic features of fetuses with Down syndrome and compared them with euploid fetuses. Patients were referred for an increased risk of aneuploidy and evaluated for the presence of structural defects, a nuchal fold, short long bones, pyelectasis, brachycephaly, small stomach, and hyperechoic bowel. Outcome information included the results of genetic amniocentesis (if performed), the results of pediatric assessment, and follow-up after birth. The sensitivity, specificity, and likelihood ratios for markers ware calculated isolated findings. RESULTS: There were 59 fetuses with Down syndrome and 600 euploid fetuses. The presence of any marker resulted in sensitivity for the detection of Down syndrome of 86.4% with a false-positive rate of 13.6%. Structural defect had a likelihood ratio of 77.8. As an isolated marker, the nuchal fold, short humerus, short femur, echogenic bowel and renal pyelectasia has a likelihood ratio of 20.2, 12.7, 3.9, 2.5, 1.1 respectively. Other isolated markers had low likelihood ratios because of the higher prevalence in the unaffected population. CONCLUSION: Combining second-trimester serum testing and fetal sonography is a feasible approach to Down syndrome screening, compatible with current obstetric practice. Although an isolated marker with a low likelihood ratio may not increase a patient's risk of Down syndrome, the presence of such a marker precludes reducing the risk of aneuploidy. This information will be useful in counseling pregnant women who are at high risk for fetal Down syndrome and who prefer to undergo genetic sonography before deciding about genetic amniocentesis.

The Distribution of Fetal Nuchal Translucency Thickness in Normal Korean Fetuses

The aim of present study was to establish normative data for the distribution of nuchal translucency (NT) thickness in normal Korean fetuses. The data were collected from pregnant women with singleton pregnancies in whom fetal ultrasound was performed and the fetal NT thickness was measured between 11 and 14 weeks of gestation. Among them, a total of 2,577 fetuses with a known normal outcome were included in this study. The distribution of multiple of median (MoM) values of the NT thickness with crown-rump length (CRL) in 10-mm intervals and the 95th percentile of MoM were calculated with the linear regression method. The present study showed that NT measurements increase with increasing CRL and a false positive rate increases with increasing gestational age. Therefore, a fixed cut-off point through the first trimester was not appropriate and each NT measurement should be examined according to the gestational age. The present study offers normative data of the fetal NT thickness in a Korean population, which can be used as reference for screening chromosomal aberrations or other congenital abnormalities in the first trimester.

A Multi-center Study for Birth Defect Monitoring Systems in Korea

The aim of this study was to establish a multi-center birth defects monitoring system to evaluate the prevalence and the serial occurrence of birth defects in Korea. Ten medical centers participated in this program. A trained nurse collected relevant records from delivery units and pediatric clinics in participating hospitals on a monthly basis. We observed 1,537 cases of birth defects among 86,622 deliveries, which included live births and stillbirths. The prevalence of birth defects was 1.8%, and the sex distribution of the birth defect cases was 55.2% male and 41.6% female. The highest proportion of birth defects was in the cardiovascular system (17.5%), followed by birth defects involving in the genitourinary system (15.6%). Chromosomal anomalies were detected 30.0 per 10,000 births. Of these chromosomal anomalies, Down syndrome was most frequently observed. This study led to an establishment of a multi-center active monitoring system for birth defects. To better understand the serial occurrence of birth defects in Korea, it is necessary to increase the number of participating hospitals and to launch on a nation-wide multi-center study.

Amniotic Fluid Interphase Fluorescence in situ Hybridization (FISH) for Detection of Aneuploidy;Experiences in 130 Prenatal Cases

The major aneuploidies diagnosed prenatally involve the autosomes 13, 18, 21, and sex chromosomes X and Y. Fluorescence in situ hybridization (FISH) allows rapid analysis of chromosome copy number in interphase cells. We retrospectively reviewed 130 amniotic fluid interphase FISH analyses from January 1997 to December 2001. The review was done in order to assess the role of interphase FISH among the patients who were at the risk of fetal aneuploidies. The sample was considered to be aneuploid when 70% of or more than the total number of hybridized nuclei displayed the same abnormal hybridization pattern for a specific probe. All of 130 cases but one met the criteria. The results were considered as informative and they were obtained in 24-48 hr. The overall detection rate for aneuploidies was 100% (2 cases of trisomy 21, 2 cases of trisomy 18, and 1 case of Turner syndrome). In comparison to cytogenetics, the rates of both sensitivity and specificity were 100%. The experiment demonstrates that FISH can provide a rapid and accurate clinical method for prenatal identification of chromosome aneuploidies. The experiment can also serve as an adjunctive test to help cytogenetics to reduce significant amount of emotional stress of patients and physicians through early decision making process.