someone please help

Baby is measuring 4 weeks smaller is that a sign of Down syndrome ? My dr. Said we can't tell until the baby is born but all the specialist ultrasounds said he looks normal but we can't know until baby is born . Please If anyone is going through this or had similar things talk to me for reassurance I'm so scared I had a difficult pregnancy and from a mom to a mom someone please talk to me . I am 35 weeks pregnant