When your employee tells you she's pregnant

When a woman announces she is pregnant to her employer, whether inwardly or outwardly the employer probably thinks ‘oh no, what are we going to do?’. 

Maternity leave is seen purely as a loss of that person for a period of time.  But it doesn’t need to be. 

On a purely financial level there is a cost associated with losing your talent, so surely every step should be taken to support the employee and protect the business from losing the vital knowledge this employee holds.