Aim: To evaluate first-trimester ductus venosus flow in relation to nuchal translucency (NT) and fetal karyotype. Methods: Ductus venosus flow was measured in fetuses with NT greater than or equal to the 95th centile (group A) and in fetuses with NT less than the 95th centile (group B). The waveforms were classified as normal if the lowest forward velocity during atrial contraction (ACV) was positive and abnormal if it was absent or negative. The results were compared with the fetal karyotype. Results: Ductus venosus measurement was carried out in 330 fetuses. In group A, there were 156 fetuses: in 4 cases, it was not possible to obtain the measurement, and in the other 152 cases, 93 (61%) had a normal ACV and 59 (39%) an abnormal ACV. NT thickness was significantly greater in fetuses with abnormal ACV. In 34 out of 156 cases (22%), chromosomal abnormalities were found. Twenty-three chromosomopathies out of 33 (70%) had an abnormal ACV, and 10 (30%) had a normal ACV. A significant association between abnormal karyotype and abnormal ACV was found. Ductus venosus measurement was carried out in 174 fetuses of group B. In 1 case, it was not possible to obtain the measurement. One hundred and seventy-one (99%) cases had a normal ACV, and in 2 (1%) cases the ACV was abnormal. No chromosomal abnormalities were found in group B. Considering group A and group B, a significant association between the finding of an enlarged NT and abnormal ACV was detected (p < 0.05). Conclusions: An abnormal ACV is more frequent in fetuses presenting enlarged NT than in those having normal NTs and in fetuses having the larger nuchal thickness. The probability of having a chromosomal abnormality in fetuses with enlarged NT is greater when an abnormal ACV is found.
Screening for chromosomal defects by measurement of nuchal translucency thickness identifies 80% of fetuses with trisomy 21 for a false-positive rate of 5%. In our population with a median maternal age of 33 years, screening by a combination of maternal age and fetal nuchal translucency thickness with a risk cut-off of 1 in 300 identified 90% of trisomy 21 pregnancies for a false-positive rate of 9%.
This paper reviews the characteristics and the results of 15 years of experience with a preventive program, based on carrier screening and prenatal diagnosis, designed to control thalassemia major in the Sardinian population. The education of the population about thalassemia and the modalities for its prevention was accomplished via the mass media. Carrier screening was carried out voluntarily on couples of child-bearing age. Prenatal diagnosis was initially carried out by fetal blood analysis; since 1983, it has been done by DNA analysis on non-amplified or amplified DNA. Different chorionic villous sampling procedures have been used. Nowadays, we have adopted the transabdominal approach because, in our experience, it seems to be associated with a low risk (2%) of fetal mortality. At the present time, the beta-thalassemia mutations are detected directly by dot-blot analysis of amplified DNA with 32P- or horseradish peroxidase-labeled allele-specific oligonucleotide probes. Two oligonucleotide probes, one complementary to the codon-39 nonsense mutation, which accounts for 95.7% of the beta-thalassemia chromosomes in the Sardinian population, and the other complementary to the frameshift at codon 6, which is the second most common mutation in our population (2.1%), allow us to make prenatal diagnosis in the large majority of cases. Notwithstanding a careful dissection of maternal decidua from chorionic villi, co-amplification of maternal sequence was detected in 4 out of 425 cases tested by this procedure. In order to avoid this pitfall, the simultaneous amplification of highly polymorphic VNTR (variable number of tandem repeats) segments could be used. On the whole we have so far carried out 2711 prenatal tests: 1130 by fetal blood analysis, 1156 by oligonucleotide hybridization on electrophoretically separated DNA fragments, and 425 by dot-blot analysis on amplified DNA with allele-specific oligonucleotide probes. Two errors occurred by fetal blood analysis and none by DNA analysis. The incidence of thalassemia major declined from 1:250 live births in the absence of prevention to 1:1000 after the establishment of this program, indicating that carrier screening and prenatal diagnosis are effective means for preventing thalassemia major at the population level.
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