The best way of diagnosing Trisomy-21 during second trimester of pregnancy is:
A. Triple marker estimationB. Nuchalskin fold thickness measurement
C. Chorionic Villus Sampling
D. Amniocentesis
Ans. D.
Amniocentesis
Prenatal
diagnosis of Downs Syndrome.
Risk
of having a fetus affected by Downs syndrome at an advanced maternal age >35
years. is well known.
USG
and biochemical markers are being used to calculate the risk and predict
outcomes. Fetal blood sampling and tissue sampling being invasive can be
performed only in very selected cases.
Currently
second trimester USG scanning has been shown to detect up to 60% ofDS fetuses.
The
following findings on USG are useful:
1.
Nuchal skin thickness measured on an axial view where the cavumseptipellucidi.
, cerebral pedicles, cerebellar
hemispheres
and cisterna magna are seen. A cut off of 6 mm is significant.
2.
Choroid plexus cysts
3.
Cardiac defects are noted in 50% children with DS.
4.
Abdominal findings namely duodenal atresia, omphalocoele, pylectasis ascites,
two vessel umbilical cord, a single umbilical artery, echogenic bowel, should
be seen. Duodenal atresia can be diagnosed as early as 14 weeks on a USG.
5.Femur,
humerus length is a possible marker of underlying trisomy 21.
Ratio
of biparietal diameter to femur length and humerus length with expected length
are good predictors with sensitivity of 37% and specificity of 47%.
6.Clinodactyhy,
hypoplastic mid phalanx in the fifth finger, increased gap between 1 st and 2nd
toe can be detected.
