Avaliação ultrassonográfica do osso nazal fetal: validação da curva de normalidade

Abstract

The noninvasive prenatal screening for aneuploidy, mostly the trisomy 21, has been improved so as to reduce the false-positive rates, allowing better indication of the invasive procedures. Among these, the ultrasound has been highlighted, the evaluation of the fetal nasal bone being one of the propedeutical tools openly spread. There is association both between the absence of the ultrasound image of the fetal nasal bone and the aneuploidies and their hypoplasia. However, there is no clear definition of what the hypoplasia of the fetal nasal bone may be. Therefore, the purpose is to validate the normal range of the length of the fetal nasal bone grown along all the pregnancy period and based on the Brazilianpopulation so as to set the cut-off that may better define such hypoplasia. It deals of an observation study, prospective, longitudinal, on propedeutic method that has evaluated 1.320 fetuses between 10 and 39 pregnancy weeks. The fetuses were divided into groups according to the pregnancy age at the time of the exams as follows: a) from 10 to 14 weeks; b) from 15 to 19 weeks; c) from 20 to 24 weeks; d) from 25 to 29 weeks; e) from 30 to 34 weeks; d) from 35 to 39 weeks. The groups were also classified as follows: a) euploid fetuses without major structural malformation from healthy mothers (normal); b) fetuses with aneuploidias (aneuploid); c) fetuses with Down syndrome (T21); d) euploid fetuses with major malformations (malformation); e) euploid fetuses, without major structural malformations whose mothers presented hypertensive disease and/or diabetes mellitus during the pregnancy (obstetric intercurrences). Conclusions: a) the normal range of the fetus nasal bone length showed accuracy for detecting aneuploid fetuses, having an ideal cut-off for each gestational age group, with tendency to a better performance, qualitative evaluation between absence and presence of the nasal bone in the group between 10 and 14 weeks and the centil2,5 for the other gestational age groups; b) it was noted more accuracy fordetecting trisomy 21 in relation to the other aneuploidias only in the group between 15 and 19 weeks; c) among the evaluated mothers and fetuses diseases, only the non-chromosomal major fetal malformations have interfered in the detection of aneuploid fetuses in the groups of 15 to 19 weeks and 20 to 24 weeks.