Di/Di Twins Baby B Measuring a week behind

Looking for any one else that has experienced this with Baby B being smaller and low amniotic fluid. This was 9 weeks 1 day but Baby B measuring 8 weeks 1 Day. Baby A is right on track. We have an appointment next week for genetic testing. Would love to hear if other Moms have experienced this. The Maternal fetal Doc is concerned about baby B and says prognosis is guarded for this baby. Thoughts?