My mum keeps making bird nest. Is there a limit to how much a pregnant mum in her 2nd trimester can drink?

Too much of anything is not good. Everything should be taken in moderation. Bird's nest has carbohydrates, protein, iron and fibre and excess will be passed out as waste. http://www.healthxchange.com.sg/answers/Pages/diet-nutrition-pregnancy-doctor-questions-answers-health-xchange-singapore.aspx