NUCHAL TRANSLUCENCY AND CARDIAC ANOMALIES

IN THE FETUS WITH NORMAL CHROMOSOMES

In the absence of a chromosomal abnormality, there is an increased incidence of cardiac anomalies in fetuses that have increased nuchal translucency

(1). The pathophysiology of this temporary anatomical sign is unknown (2).

Table of frequency of cardiac defects in chromosomally normal fetuses with increased nuchal translucency.

Normal developmental events:

• Lymphatic pathway establishes it definitive connection with the jugular sinuses at 10-14 weeks gestation.
• The arterial tree of the upper limb develops from about 11 weeks gestation.
• The fetal heart matures and changes from a symmetrical to asymmetrical vascular system.
• In the normal fetus there is a physiological variation in nuchal translucency and gestational age. The translucency generally disappears by 14 weeks gestation (3).

Exaggeration of the normal physiological nuchal fluid collection may be due to a genetic, structural or infectious cause (4).

Workers (1) have suggested that this excess accumulation of nuchal fluid may be due to temporary heart failure. Increased atrial pressure at end diastole, venous regurgitation and reversal of flow in the ductus venosus and inferior vena cava. In the third trimester this usually is indicative of severe hypoxia, anemia or supraventricular tachycardia. Reversed flow in the umbilical artery has been described in two out of six fetuses with trisomy 18 at 10 weeks gestation. An increased nuchal translucency was present in both fetuses (5).

Reversed flow in the ductus at 13 weeks in a fetus with trisomy 18 and an increased nuchal translucency has been described (4). Hyett and co-workers (6) have demonstrated cardiac defects in all trisomy 18 fetuses and hypothesized that unperforated valves and hypoplastic great vessels may cause venous congestion and excessive fluid accumulation in the nuchal area. Spontaneous resolution of the nuchal translucency is common and probably due to the correction of the hemodynamic disturbance later in the gestation (6).

Narrowing of the aortic isthmus has been found at post-mortem examination to be a common finding in chromosomally normal and abnormal fetuses with increased nuchal translucency (1,6). Septal defects are usually a transient finding that close in utero (7). Normalization of ductus venous flow later in the gestation supports the hypothesis that the hemodynamic disturbance correct in utero.

REFERENCES

1. Hyett J, Moscoso G, Papapanagiotou G, et.al. Abnormalities of the heart and great arteries in chromosomally normal fetuses with increased nuchal translucency thickness at 11-13 weeks of gestation. Ultrasound Obstet Gynecol 1996;7:245-250.
2. Moscoso G. Fetal nuchal translucency: a need to understand the physiological basis. Ultrasound Obstet Gynecol 1995;5:6-8.
3. Pajkrt E, Bilardo CM, van Lith JMM et.al. Nuchal translucency measurement in normal fetuses. Obstet Gynecol 1995;86:994-997.
4. Huisman TWA, Bilardo CM. Transient increase in nuchal translucency and reversed end-diastolic ductus venosus flow in a fetus with trisomy 18. Ultrasound Obstet Gynecol 1997;10:397-399.
5. Martinez Crespo JM, Comas C, Borell A et.al. Reversed end-diastolic umbilical artery velocity in two cases of trisomy 18 at 10 weeks gestation. Ultrasound Obstet Gynecol 1996;7:447-449.
6. Hyett J, Moscoso G, Nicolaides KH. Abnormalities of the heart and great arteries in first trimester chromosomally abnormal fetuses. Am J Med Genet 1997;69:207-216.
7. Nir A, Weintraub Z, Oliven A et.al. Anatomic evidence of spontaneous intrauterine closure of a ventricular septal defect. Pediatr Cardiol 1990;11:208-210.