Nasal bone in screening for trisomy 21: defining hypoplasia

Prenatal screening for genetic disorders: updated guidelines, proposed counseling, a holistic approach for primary health care providers in developing countries

Prenatal screening (PNS) can be a very effective strategy for identifying the individuals at-risk of genetic disorders. In contrast to prenatal genetic tests, which are very expensive, require special set-ups and expertise, PNS can be of great help in reducing the burden of genetic disorders, especially in the Indian context. During the last 10 years, several advanced PNS tests utilizing new platforms, with comparatively more sensitivity and specificity, have emerged. PNS tests for chromosomal aneuploidies, microdeletion syndromes, hemoglobinopathies, neural tube defects etc. are available. However, primary health care providers need to be made more aware about the availability of different tests, the time point at which these need to be used, appropriateness of these tests to various presentations and interpretation of the result. They need to be periodically informed about the availability, limitations, sensitivity and specificity of different platforms for PNS. Further, there is a need to develop uniform, updated and practical guidelines on PNS and disseminate these to health care providers so as to benefit the mass population. This article compiles information on different types of PNS and prenatal diagnostic tests, commonly required for different genetic conditions. These recommendations may help clinicians and primary healthcare providers in PNS.

Magnetic resonance imaging evaluation of fetal maxillary sinuses

BACKGROUND AND OBJECTIVE

The growth of maxillary sinus is closely connected to the development of facial structures. However, its definition and reference standards on fetal magnetic resonance imaging (MRI) have not been analyzed so far. In this study, the objectives were to define and evaluate the fetal maxillary sinus (fMS) formation with MRI.

METHODS

We reviewed T2-weighted coronal MRI images of 75 fetuses. The MRI features, time of appearance, and boundaries of fMS were defined. Craniocaudal and transverse diameters of both maxillary sinuses and bone biparietal diameters were measured and statistically evaluated.

RESULTS

In 150 fMS site analysis, 91 fMSs were identified. The fMSs were visualized as a hyperintense structures on T2-weighted image above the tooth bud. It first appeared at the 22nd gestational week, and in 4% (3/75) of fetuses, there was unilateral development. Mean craniocaudal length was 2.84 mm (1.1-4.8 mm), and mean transverse diameter was 2.67 mm (1.5-4.2 mm).

CONCLUSIONS

Magnetic resonance imaging features of fMS that should be sought for the assessment of craniofacial anatomy are identified in this study. Fetal maxillary sinuses can be observed as hyperintense structures on T2-weighted MRI images starting from 22 weeks of gestation. The growth of fMS follows a predictable course throughout gestation; however, the dimensions are larger than the previously reported ex vivo series.

Nasal bone in prenatal trisomy 21 screening

The definitive diagnosis of fetal chromosomal abnormalities is only accomplished through tests that sample fetal tissue. These procedures--amniocentesis, chorionic villus sampling and cordocentesis--are invasive and carry with them the risks of bleeding, rupture of membranes, and even pregnancy loss. Current recommendations from the American College of Obstetricians and Gynecologists state that all women should be offered screening, regardless of maternal age. However, the exact screening test to apply to pregnant women is still a matter of debate. The goal of any screening method should be high detection (sensitivity) at low screen positive rates. Recent attention has focused on additional ultrasound markers to potentially improve the detection rate. Given that mid-face hypoplasia and a flattened nose are characteristic features of Down syndrome, investigators have tried to utilize its prenatal appearance--or more specifically, its absence--to enhance the detection of trisomy 21 (T21). The purpose of this document is to review the data on the utility of the nasal bone as a marker for T21. Particular attention will focus on its use in the first trimester versus second trimester as well as future directions for its potential incorporation into screening strategies.

TARGET AUDIENCE

Obstetricians & Gynecologists, Family Physicians.

LEARNING OBJECTIVES

After completion of this article, the reader will be able to relate the prenatal and postnatal nasal phenotypes for Down syndrome, identify the potential role and pitfalls of nasal bone characteristics in screening for Down syndrome, and describe 3 different methods to define fetal nasal bone hypoplasia.

First-trimester ultrasound: current uses and applications

This article is aimed to aid the sonographer and medical care provider in better interpretation and clinical application of first-trimester ultrasound findings in early pregnancy. We review current uses, applications, and interpretations of first-trimester ultrasound. A discussion of basic embryology and normal as well as abnormal first-trimester sonographic findings are discussed. We also cover the utility of the first-trimester ultrasound in screening for fetal aneuploidy. Attention is also given to the role of the first-trimester ultrasound in the prediction of adverse perinatal and maternal outcomes.