From what I was told with low papp a if the growth is being restricted due to low papp a the head will be larger than the rest of the body because our bodies magically know that it is important for the brain to develop so the head has priority over the rest of the body.
I made it to 37weeks, this is when
DD stopped growing. At one stage it looked like we would have to deliver at 32wks but then things improved so we could go longer.