Nuchal dating scan nhs
As of 2015, there are five commercial versions of this screen (called cell-free fetal DNA screening) available in the United States.Blood testing is also used to look for abnormal levels of alphafetoprotein or hormones.However this procedure carries a small risk of miscarriage so prior screening with low false positive rates are needed to minimize the chance of miscarrying.The actual anatomic structure whose fluid is seen as translucency is likely the normal skin at the back of the neck, which either may become edematous or in some cases filled with fluid by dilated lymphatic sacs due to altered normal embryological connections.The results of all three factors may indicate a higher risk.If this is the case, the woman may be advised to have a more reliable screen such as cell-free fetal DNA screening or an invasive diagnostic test (such as chorionic villus sampling or amniocentesis).Progressive increase in the width of the translucent area during the 11- to 14-week measurement period is thus indicative of congenital lymphedema.Nuchal translucency testing is distinctly different from and should not be confused with nuchal thickness testing.
Nuchal scan (NT procedure) is performed between 11 and 14 weeks of gestation, because the accuracy is best in this period.
Among those fetuses whose nuchal translucency exceeds the normal values, there is a relatively high risk of significant abnormality.
An increased nuchal translucency increases the probability that the fetus will be affected by a chromosomal abnormality, congenital cardiac defects, or intrauterine fetal demise.
Screening for Down syndrome by a combination of maternal age and thickness of nuchal translucency in the fetus at 11–14 weeks of gestation was introduced in the 1990s.
This method identifies about 75% of affected fetuses while screening about 5% of pregnancies.