The British Medical Association has said pregnant women should not be called "expectant mothers" as it could offend transgender people.
Instead, they should call them "pregnant people" so as not to upset intersex and transgender men, the union has said.
The advice comes in an internal document to staff outlining a raft of common phrases that should be avoided for fear of causing offence.
The elderly" should be referred to as "older people", "disabled lifts" called "accessible lifts" and someone who is "biologically male or female" should be called "assigned male or female".
The BMA said the document was purely guidance for its staff on effective communication within the workplace, not advice to its 156,000 doctor members on how to deal with patients.
On pregnancy and maternity, it says: "Gender inequality is reflected in traditional ideas about the roles of women and men. Though they have shifted over time, the assumptions and stereotypes that underpin those ideas are often deeply-rooted."
It adds: "A large majority of people that have been pregnant or have given birth identify as women. We can include intersex men and transmen who may get pregnant by saying 'pregnant people' instead of 'expectant mothers'."
It recently emerged that a Briton who was born a girl but wants to become a man has put surgery on hold in order to have a baby.
Hayden Cross, 20, is legally male and had hormone treatment but not yet had sex-change surgery.
There are no other known cases of a transitioning person becoming pregnant in the UK.
The guide also advises against using the terms "born man" or "born woman" in relation to trans people, as these phrases "are reductive and over-simplify a complex subject".
Elsewhere, staff are told to substitute the words "surname" or "last name" for "family name".
"Mankind" and "manpower" should be avoided because it is "not good practice" to use a "masculine noun", instead swapped for "humanity" and "personnel", and listing prefixes for names such as "Prof", "Dr", "Mr", "Mrs" or "Miss" should not be put in a particular order on forms to avoid a "perceived hierarchy".
The document, which was published last year, also underlines guidance on language that has long been considered offensive, suggesting staff do not refer to people as being "spastic" or "mongol" but that they should be called a "person with cerebral palsy" or "person with Down's syndrome".
The advice came in a 14-page leaflet, called A Guide to Effective Communication: Inclusive Language in the Workplace.
The introduction to the document states: "This guide promotes good practice through the use of language that shows respect for and sensitivity towards everyone. The choice of appropriate words makes an important contribution towards the celebration of diversity.
"As well as avoiding offence, it is about treating each other with dignity and as equal members of an integrated community."
A BMA spokesman said: "This is a guide for BMA staff and representatives aimed at promoting an inclusive workplace at the BMA. It is not workplace guidance for doctors which is clear from the fact it does not refer to patients."
Conservative MP Philip Davies described the guidance as "completely ridiculous".
He said: "If you can’t call a pregnant woman an expectant mother, then what is the world coming to?"
Michael Nazir-Ali, the former Bishop of Rochester, told The Mail on Sunday: "I think it is sad that society is being pushed in this direction. God has made us man and woman, and mothers relate to their children in different ways than fathers. This ruling will confuse people about the vital role of mothers in bringing up their children."
The Roman Catholic Bishop of Portsmouth, the Right Reverend Philip Egan, warned it would cause "great confusion and harm".
He said: "It is Orwellian, isn’t it? Another example of people trying to control our thoughts and the way we speak."
However, Heather Ashton, from the transgender support group TG Pals, said: "We know that biological females are the pregnant ones but trans people are parents too, and this is massive step forward to prevent discrimination against them. The fact that the terminology is changing can only be a positive thing for everyone who wants to be a parent and has the right to be a parent."