hello doc, im 17weeks pregnant. my 17 weeks ultrasound repoet is that placenta is posteriore and of grade1 maturaity. liquore is adeqate for the gestational age , cervacal length is 36.2mm internal os is closed. my fetal measurment is BPD 37.3MM, H. CIR IS 136.6MM, AB CIRC 116.1MM AND FL IS 25.1MJM. THE ESTIMATED FETAL WEIGHT IS 195G PLUS 29G. BUT THE DOC TELL ME TO DO A DOWN SYNDROM TEST SO AS PER MY ULTRASOUND REPORT IS IT ANY PROBLEM OR SIGN OF DOWN SYNDROM.