How to make near accurate   risk calculation for aneuploidy risk calculation ?? Both patient and sonologist must be honest and air in their statements  and Observations.Then only statistical risk probably can be assessed  with fair degree of accuracy.  Ans: First trimester screening for  prenatal   risk assessment of unborn   baby for   disorders  like trisomy 18, trisomy 21,  trisomy 13 is recommended   for all pregnant women to identify women   at significant   risk for the above   mentioned  anomalies  in the fetus  to warrant   timely evaluation   and follow up .But  to achieve near  100%  statistical  evaluation one has to furnish at least eight types of data in the software and then only risk possibility can be assed. The interpretive unit    is MoM   considers variables such as gestational age , maternal age, race,  weight   diabetes mellitus,  multiple gestation, smoking  history  , drug history   , ultrasound   findings.. However different software are used by diff Lab   and sadly not all are approved by FMF(Foetal medicine Foundation). One of the relatively uncommon software is  has been done  using Benetech PRA software. Maternal  screening  tests  are based on statistical analysis   of patient    demographic  and biochemical  data. They simply indicate a low or high risk. Risk calculation  based on statistical software has no diagnostic   value . Screening cut off are established by using  MoM values      that maximize the detection rate and minimize false   positive  rates. Confirmation of screen positives  is recommend  in amniotic   fluid. Accurate   availability   of data mentioned above  and others   is a must   for correct risk calculation . Ideal age for  dual marker  testing is between 10-13 weeks of gestation though   it holds   valid between   9-13.6 weeks of gestation .