Mrs Beehcham, the dental nurse, should know even then, that she would break the patients confidentiality. Although Mrs Warrender did say she was a wicked spiteful woman who would take the opportunity to point score over the Warrenders that keeping quiet.
Its unusual that Vincent calls his mother "Reet" instead of Mum (or similar word) suggesting shes his step mother. At the dinner party she confirms that she is his actual mother by describing the pregnancy and "Reet" is just an affectionate name her calls her.