Ultrasound diagnostic schema for the determination of increased risk for chromosomal fetal aneuploidies in the first half of pregnancy.

The aim of the study was to develop an early ultrasound diagnostic schema for the determination of increased risk for fetal chromosomal aneuploidies. The study was conducted on a population of 1318 pregnant women divided into 2 groups: 1255 women with the normal course of pregnancy and 63 women with diagnosed fetal abnormalities. There were 34 cases of chromosomal abnormalities (trisomy 21, 18, 13; triploidy; unbalanced inversion 9; deletion 16) and 29 cases of structural malformations. The estimation of the range of normal values was performed for the nuchal translucency (NT) measurement between 11 and 13 weeks and the nasal bone length (NB) measurement between 12 and 20 week. The results obtained in the collective set of normal pregnancies constituted the basis for the calculation of the range of normal values. The measurements of NB and NT showed a linear value increase with the pregnancy course. The following test characteristics (correlation to CRL) were recorded: NB - sensitivity 60%, specificity 98%, positive predictive value (PPV+) 43%, negative predictive value (NPV-) 98.9%. For the assumption that the test outcome means the presence or absence of the nasal bone in the ultrasound scan the sensitivity was 40%, but specificity 100%; NT - sensitivity 63.6%, specificity 98.2%, PPV+ 38.9%, NPV - 98.2%; NT + NB - presents similar characteristic to the NB or NT alone - sensitivity 55.6%, specificity 98.6%, PPV+ 50%, NPV - 98.9%. The following test characteristics for chromosomal aberration markers (correlation to BPD) were observed: NB - sensitivity 68.4%, specificity 97.4%, PPV+ 56.5%, NPV - 98.4%; NT - sensitivity 73.9%, specificity 97.9%, PPV+ 54.8%, NPV- 99.2%; NT + NB - sensitivity 94.7%, specificity 98.9%, PPV+ 90%, NPV - 99.7%, respectively. The "genetic sonogram" protocol for the structural defect detection was analysed: sensitivity was 80%, specificity 100%, PPV+ 100%, NPV - 99.7%. It is concluded that the new biometric parameter--nasal bone length (NB) and the corrected one--nuchal translucency thickness (NT) are useful markers for fetal abnormalities, especially for chromosomal aberrations. High predictive values of the diagnostic schema for the detection of aneuploidies and structural defects indicate that its application in correlation with the biparietal diameter (BPD) is highly recommended. The proposed schema is an effective algorithm for prenatal diagnostics characterised by high prognostic values. The possible introduction of the schema could result in a decrease of the invasive procedure rates, which could minimise the rate of miscarriages as a complication of amniocenteses.