The 26-year-old's message on the micro-blogging site Twitter was posted on April 1, suggesting the actress could be playing a April Fools' Day joke, reported TMZ Online.
"Its official. Pregnant," Lohan tweeted to her six million followers. When one of her followers commented, "I'm not paying child support bb sry bye," she jokingly replied, "Thanks dad - you do look like a man a bit."
The posting has been re-tweeted by more than 10,000 users and has become a worldwide trending topic.
Lohan, who is expected to enter a 90 day rehab facility in May due to charges stemming from a car crash, is currently dating City of the Sun's rocker Avi Snow.
According to reports, flight crew was afraid that there was chemical leak or possible sabotage after they smelt a "toxic odour" emitting near the front of the plane. Turned out, the potential hazardous material was nothing but a "biohazard" left by someone in the first class lavatory.
She was in Brazil to support the opening of John John Denim's flagship store in Sao Paulo.