IgG antibodies can cross the placenta, leading to thyroid enlargement. This can also explain the stridor and issues with respiration in the newborn. Essentially, this is causing neonatal Graves disease.
From UpToDate: "Neonatal Graves disease refers to the hyperthyroidism that is seen in a small percentage of infants born to mothers with Graves disease. Although neonatal Graves disease is usually self-limited, it can be severe, even life-threatening, and have deleterious effects on neural development"
Hyperthyroidism in the newborn