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POSSIBLE MECHANISMS OF INCREASED NUCHAL TRANSLUCENCY |
- Cardiac failure associated with abnormalities of the heart and great vessels.
- Septal or valvular defects (43%).
- Narrowing of the aortic isthmus and narrowing immediately above the aortic valve (86%) (1).
- Venous congestion in the head and neck.
- Constriction of the fetal body (amnion rupture sequence).
- Superior mediastinal compression (diaphragmatic hernia).
- Narrow thoracic cavity (skeletal dysplasia e.g. Thanatophoric dwarfism).
- Failure of lymphatic drainage due to abnormal or delayed development of the lymphatic system (2).
- Impaired fetal movements.
- Fetal neuromuscular disorders.
- Altered composition of subcutaneous connective tissue.
- Fetal anemia or hypoproteinemia.
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DUCTUS VENOSUS BLOOD FLOW AND NUCHAL TRANSLUCENCY |
The ductus venosus is a unique shunt that carries well oxygenated blood from the umbilical vein directly into the cerebral and coronary circulation. It has a high pulsatile forward flow throughout the cardiac cycle, and appears to be useful in assessing cardiac function.
Link to the normal Ductus Venosus
In situations of cardiac failure in the late second and third trimesters, with or without cardiac defects, reversed flow during atrial contraction (A wave) may be present. In the first trimester, this may be a normal finding prior to 15 weeks of gestation, however in the presence of increased nuchal translucency, this may be due to cardiac dysfunction due to an underlying cardiac defect. It has been suggested that there may be a temporary functional abnormality either in the ventricles, aortic outflow tract or ductus itself. We have personally demonstrated an increased frequency of left sided cardiac defects (hypoplastic LV and coarctation of the aorta).
Down syndrome –
Increased nuchal
translucency + reversed A wave in the ductus venosus |
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Absent A wave
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Reverse A wave
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REFERENCES |
- Hyett JA, Moscoso G, Papapanagiotou G et.al. Abnormalities of the heart and great vessels in chromosomally normal fetuses with increased nuchal translucency thickness at 11-13 weeks of gestation. Ultrasound Obstet Gynecol 1996;7:245-250.
- Greco P, Loverro G, Vimercati A et.al. Pathological significance of first trimester fetal nuchal edema. Prenat Diagn 1996;16:503-509.