The yoga instructor - who married Baldwin in June - accused the media of making women self-conscious of their weight by constantly speculating about celebrity pregnancies.
"[Should] rumours that I'm pregnant give me a cmplx (sic) about my waistline? 1 of the biggest culprits in the eating disorder epidemic is the media," Thomas tweeted on Tuesday (August 28).
She continued: "How slim do u have to be? This is a serious problem in society. How about this: when I'm pregnant, I'll tell you… Deal?"
Baldwin's daughter Ireland also recently hit out at the media by claiming that they "lie about everything".
The 30 Rock actor made headlines in June as well by confronting a photographer outside of New York City's marriage licence bureau.
He later denied accusations that he struck the paparazzo.