CLINICAL AND ULTRASONOGRAPHIC FINDINGS OF FETUSES WITH TRISOMY 21, 18 AND 13 CASES DIAGNOSED PRENATALLY IN AMNIOTIC FLUID SAMPLES. FROM JANUARY 1989 TO JULY 2010, 142 TRISOMY 21, 39 TRISOMY 18, 12 TRISOMY 13 CASES WERE DIAGNOSED IN AMNIOTIC FLUID SAMPLES