My wife(25 yrs, 20 weeks pregnant) did ultrasound 5D test, in which fetus nasal bone appeared small (4.5mms). Other parameters & NT scan are normal. Now doctor asked us to go for quadraple marker test from which we can know any other defects. But is it the strong symptom of down syndrome? Or is there any other test by which we can identify the down syndrome perfectly? Do we need to worry about this?