Is it permissible for people to ask about extremely private matters such as pregnancy, and are the spouses required to announce the pregnancy, or is it a private matter that can be kept confidential?

Overstepping proper manners when speaking with others stems from ignorance, a lack of attention to noble character, and interfering in matters that do not concern one. The saying of the Messenger of Allah, peace and blessings be upon him: "From the excellence of a person's Islam is his leaving what does not concern him," is a great principle in etiquette. So, from the excellence of one's Islam is his leaving what does not concern him, whether in word or deed, and limiting himself to what does concern him. This includes safeguarding the tongue from idle talk, for "every word of the son of Adam is against him, not for him, except enjoining good, forbidding evil, and remembering Allah, the Mighty and Exalted." This etiquette was a path for the predecessors of the Ummah.