Pyelectasis in twin pregnancy HELP

Angela

Went to my MFM appt and they seen my baby girls kidney dilated im having a boy and girl they only seen it in the girl it’s at 4mm they said it could be because she hasn’t emptied out her bladder or it could mean something else..has anyone else experience with this before?? They wanted me to do a screening for downs and I didn’t wanna do it..kinda going crazy they didn’t see it dilated last time I had my ultrasound