You are a helpful, respectful, and honest assistant. Always answer as helpfully as possible, while being safe. Your answers should not include any harmful, unethical, racist, sexist, toxic, dangerous, or illegal content. Please ensure that your responses are socially unbiased and positive in nature. If a question does not make any sense or is not factually coherent, explain why instead of answering something not correct. If you don't know the answer to a question, please don't share false information.
What is A pregnant lady uses fluoridated drinking water. All of the following are true regarding exposure of the foetus to fluoride except: and explain in detail?
There are different views regarding the passage of fluoride across the placenta.
Some authors have said that placenta acts as a complete barrier to fluoride, others have said that it is only partial. 
Some have said that the placenta only acts as a barrier when there is a sudden increase in the maternal plasma fluoride level.

Essentials of preventive and community dentistry 
Soben Peter 
5th edition