Nuchal translucency measurement at different crown-rump lengths along the 10- to 14-week period for Down syndrome screening.

OBJECTIVES: To evaluate the screening accuracy for Down syndrome of nuchal translucency (NT) measurement at different crown-rump length (CRL) subgroups along the 10- to 14-week period. METHODS: NT was classified 'enlarged' if greater than or equal to 1.5 and 2.0 multiples of the regressed median. Accuracies for Down syndrome (formula=[(TP + TN)/(TP + TN + FP + FN)]x100, where TP: true positive, TN: true negative, FP: false positive, FN: false negative) were evaluated in four classes of CRL: 38-44 mm, 45-54 mm, 55-70 mm, and 71-84 mm, and compared. RESULTS: Of 20 743 fetuses, 20 611 were with no chromosomal abnormalities and 132 were with Down syndrome. Down syndrome fetuses with enlarged NT were 99 (greater than or equal to 1.5 MoM) and 86 (greater than or equal to 2.0 MoM). Sensitivity decreased with gestation, while specificity increased, resulting in increasing likelihood ratios with gestation for each of the CRL groups (8.1, 14.1, 16.3, 17.1 with the use of the 1.5 MoM cut-off, and 13.2, 27.1, 50.1, 84.1 for the 2.0 MoM cut-off). The accuracy increased with gestation (89%, 95%, 95%, 96% with the use of the 1.5 MoM cut-off, and 94%, 97%, 98%, 99% for the 2.0 MoM cut-off, for each of the CRL groups), differences being statistically significant between periods in half of the comparisons. CONCLUSIONS: Although sensitivity of NT assessment for Down syndrome screening decreased as gestation advanced from the 10th to the 14th week, accuracy showed a remarkable increase. These changes should be taken into account in defining and improving the Down syndrome screening policies.

Absence of fetal nasal bone and aneuploidies at first-trimester nuchal translucency screening in unselected pregnancies.

OBJECTIVES: The absence of nasal bone (NB) has been noted in trisomy 21 fetuses at first-trimester ultrasound, in high-risk pregnancies. In this study, the nasal bone was evaluated in relation to fetal karyotype, in unselected pregnancies. METHODS: From September 2001 to September 2002, the fetal facial profile was examined at the 11 to 14 weeks' scan for screening by nuchal translucency (NT). Risks for trisomy 21 were calculated using the Fetal Medicine Foundation's software, and the presence or absence of NB was noted. Prenatal karyotype and pregnancy outcomes were recorded. RESULTS: NT screening was performed in 5532 fetuses from 5425 pregnancies (85 twins, 8 triplets, 2 quadruplets). The visualization of fetal profile was obtained in 5525 fetuses (99.8%), and in 5491 fetuses (99.4%) the NB was present and in 34 cases (0.6%) it was absent. Fetal karyotype and pregnancy outcome were available in 3503 pregnancies, and 40 chromosomal abnormalities were diagnosed (27 trisomies 21, 5 trisomies 18, 2 trisomies 13, 3 Turner syndromes, 1 partial trisomy 9 and 2 others). The NB was absent in 19 (70%) trisomies 21, 4 trisomies 18 (80%), 2 Turner syndromes (66%), in the partial trisomy 9, in 7 normal karyotype fetuses (0.2%), and in a case with spontaneous first-trimester abortion before prenatal diagnosis. A significant difference was found between NT thickness, expressed as a multiple of the median, in trisomy 21 fetuses with present and absent nasal bone. CONCLUSIONS: The absence of NB at 11 to 14 weeks is more frequent in fetuses with trisomy 21 and other aneuploidies than in normal karyotype fetuses.

Neural tube defects in the offspring of thalassemia carriers.

OBJECTIVES: The risk of neural tube defects (NTDs) is negatively correlated with maternal folate levels in early pregnancy. Thalassemia carriers often have reduced red cell folate contents. The aim of this study was to verify whether thalassemia carriers are at increased risk of having offspring with a NTD. METHODS: We retrospectively evaluated the prevalence of thalassemia carriers among 75 women who had prenatal diagnoses of NTDs made at our center. RESULTS: The prevalence of beta-thalassemia carriers among the affected pregnancies was significantly higher than in the general population (22.5 versus 14%, p < 0.05, chi(2) test). CONCLUSION: Although inconclusive, these data indicate that folate supplementation is mandatory among women with thalassemia who are planning a pregnancy.