in Iran, this way is done with amniosentesis way. it is done between 15 – 17 week of pregnancy. this action is done with syringe, that sucks alittle water of amoniak that surrounded fetues. this water contains carytip. carutips are cells that contains genetic information of fetues. they send these cells for screening. screening determine that fetues has any genetic disorder or not. if anybody has any information about this, please share with others.