My gynae has advised me not to carry any weights. Does anyone know how many kgs is dangerous? Is picking up my niece who weighs 10kg not safe?

By "carry weights", do you mean exercise-wise? Generally I've been told that it's best not to carry (too) heavy objects when pregnant because you could strain your back and pelvis. Here are some ways you can exercise in your first trimester: http://sg.theasianparent.com/pregnancy-questions-can-i-exercise/