When in Pregnancy TBG is increased leading to increase in total T3 & T4, why aren't Free T3 and T4 reduced?

When in Pregnancy TBG is increased leading to increase in total T3 & T4, why aren’t Free T3 and T4 reduced?

Increased tbg binds with increased levels of t3, t4 . So free t3, t4 levels remain normal . Or reduced