PTU has stopped being recommended in pregnant women and children due to hepatotoxicity even in the first month. Methimazole is indicated for both children and pregnant women in 2019. Carbimazole is a possible alternative in some cases.
this systematic review and meta-analysis study defines the safety of PTU over CMZ in pregnant thyrotoxic ladies ( doi: 10.1371/journal.pone.0180108. eCollection 2017).