Abstract
The aim of this study was to evaluate pregnancy and postnatal outcomes of fetuses with increased nuchal translucency thickness (NT) and normal karyotype. Two hundred seventy five fetuses with increased NT were examined with karyotyping analysis, serial ultrasound scans, echocardiography and postnatal clinical and genetic evaluation at the Fetal Medicine Unit - Department of Obstetrics - São Paulo University. The karyotype was abnormal in 14.2% of the cases and normal in 85.8%. In cases with normal karyotype 24.7% presented structural abnormalities at the anomaly scan, one third of these were major malformations with 35.7% of heart defects. Adverse pregnancy outcome such as miscarriages, intrauterine and neonatal deaths occurred in 10.2% of cases. Of the infants 72.7% had postnatal examination, with 14.8% presenting abnormalities. Chances of having a live and healthy child decreased with increased NT thickness, and were of 37.5% for NT above 4.5mm. In cases with increased NT thickness and normal karyotype, the frequency of fetal malformations, especially heart defects, adverse pregnancy outcome and postnatal abnormalities is related to the NT thickness.
Highlights
Increased nuchal translucency (NT) is a common phenotypic expression in chromosomally abnormal fetuses and in those with structural malformations and genetic syndromes.[1]
As to the presence of major structural malformation it was observed that the group with NT thickness equal to or greater than 4.5 mm had larger percentage values than other groups, and these percentage values increased as the NT cutoff levels increased (p = 0.005; Fisher’s exact test)
This corroborates the findings of studies that assessed increased NT in fetuses with normal karyotype and found variability in the association with structural malformations, heart defects, ranging from 4.8 to 32.1%.8,10,11,18,19, In the present study, the chances of major structural malformation, detected in the prenatal period, grew as NT increased, and proportions were close to the ones described by other authors.[1,6,7]
Summary
Increased nuchal translucency (NT) is a common phenotypic expression in chromosomally abnormal fetuses and in those with structural malformations and genetic syndromes.[1] Possible mechanisms whereby these increases may occur include cardiac dysfunctions associated with heart defects and large arteries, head and neck venous congestion, abnormal composition of the extracellular matrix, lymphatic drainage failure caused by abnormal or late development of the lymphatic system, limited fetal movements, fetal anemia or hypoproteinemia and congenital infections.[2]. Increased NT is found in 4.4% of chromosomally normal fetuses, which are at a significant risk of fetal malformations, skeletal dysplasia, genetic syndromes and delayed brain development. The prevalence of fetal abnormalities and adverse pregnancy outcomes increases exponentially with the thickness of NT, especially when it becomes as thick as 3.5 mm.[1,5] The number of major fetal malformations (FM) rises from 2.5% to nearly 45% and the miscarriage rate and fetal death go from 8 to 80% when NT increases by 6.5 mm or more between the 95th and 99th percentiles, respectively.[1,2,4,6]
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