Are you diabetic? Have high blood pressure? Both of these cab cause smaller babies (everyone hears about big babies with diabetes but small babies are possible to). My lo measured small, so they tested me for other diseases, like herpes. But downs is also a possibility. It honestly could be nothing as well. I know it is hard not knowing why.
They told me that my son was small at 38 weeks and ordered an additional ultrasound. At the ultrasound, I was told that my son was going to be big. Then he was born at 6lbs 9oz. Measuring during late pregnancy is often inaccurate for a variety of reasons. Unless baby is measuring significantly smaller, she is okay.
Not sure why your baby will be small and I'm sorry you have to go threw that but idk just stay positive hun did she say the baby had any problems if not I won't worry to much that will bring stress to you just enjoy the few days you have left may god bless you and your unborn baby ☺