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?

The amount of weight that a person can safely carry during her pregnancy depends on individual conditions. I have seen mommies who attend gym and carried weights throughout her pregnancy. However, for your case, since your Gynae has advised you not to carry weights, it will be safer to follow as it may be due to your physical condition. I will advise that you to avoid carrying your niece since she may move and kick which can be a little dangerous. You may want to consult your Gynae whether is it due to certain reason that he/she advised you not to carry weights? If yes, how heavy can you carry. For the time being, it's better to stay safe by avoiding heavy items.