Hi, TIFFA scan is targeted imaging for fetal anomalies. It is done to detect any genetic or chromosomal anomalies by visualizing the external and internal anatomy of the fetus. Thus, both major and minor anomalies can be identified as are subtle markers for certain diseases. Trisomy test is a genetic test to check for chromosomal anomalies, most commonly DOWN S syndrome and EDWARDS syndrome. It detects the AFP, estriol ans serum beta-hCG levels. Hope this helps.