The variables affecting nuchal skin-fold thickness in mid-trimester.

Abstract

To find out variables that have an effect on the measured values of nuchal skin-fold thickness (NT) and to formulate a regression equation on the basis of those variables. The data on gestational age (GA), cephalic index (CI), presentation (Pr, vertex or breech), and the presence or absence of nuchal cord (NC) were collected prospectively on 548 normal singleton fetuses between 16 and 24 weeks gestation, and independent correlation of those variables with NT was calculated by multiple regression analysis and a regression equation was produced. GA had positive correlation and CI had negative correlation with NT. The nuchal skin-fold was thicker among fetuses with breech presentation rather than those with vertex presentation and increased in the presence of nuchal cord. We calculated the expected NT through these observations: for fetuses presenting vertex, NT = 5.608 + 0.243GA - 0.066CI + NC* and for breech, NT = 2.803 + 0.392GA - 0.066CI + NC*. This is the first report, which takes GA, CI, Pr, and NC for correlation factors with NT as a whole. These equations and further studies on determining the cutoff values of the nuchal skin-fold thickness may improve the sensitivity and specificity for the detection of Down syndrome and enable to minimize unnecessary invasive procedures such as amniocentesis or cordocentesis.