Hallow Kalyani, I have gone through your query and have understood your dilemma. TIFFA scan also known as Targeted Imaging For Foetal Anomalies is performed during second trimester (13 weeks to 28 weeks) for assessing the foetus for any developmental anomalies. You have thyroid problem. Is it hypothyroidism or hyperthyroidism? Most likely it would be hypothyroidism. In this condition, the foetal developmental anomalies may be there. Moreover, you are not perceiving any foetal movements even at 20 weeks (though during first pregnancy they may be perceived some what later). Therefore your Obstetrician have asked for TIFFA Scan. Initial regular ultrasonography scan will reveal whether the foetal heart activity is seen or not and then TIFFA Scan will try to look for any abnormalities. I hope I have given you sufficient information you requested for.