The statement comes in Britain's official submission on proposed amendments to the International Covenant on Civil and Political Rights, to which the UK has been a signatory since 1976.
The UN treaty says a "pregnant woman" must be protected, including not being subject to the death penalty.
In the Foreign and Commonwealth Office (FCO) submission, Britain opposes the term "pregnant woman" because it may "exclude transgender people who have given birth".
The suggested term is "pregnant people", the Sunday Times reported.
"We requested that the UN human rights committee made it clear that the same right [to life for pregnant women] extends to pregnant transgender people," an FCO statement said.
The UN covenant is part of the International Bill of Human Rights. It undergoes periodic revision, with the latest UK submission part of the revising process.
But a feminist author has branded the move as anti-women.
"This isn't inclusion. This is making women unmentionable. Having a female body and knowing what that means for reproduction doesn't make you 'exclusionary'.
Forcing us to decorously scrub out any reference to our sex on pain of being called bigots is an insult," said Sarah Ditum.
The latest development follows a revelation by the newspaper last week that the UK's Office of National Statistics (ONS) has suggested making the sex question in the next census voluntary because it "discriminates" against trans people.
That proposal had also triggered protests from feminist authors.
Prime Minister Theresa May had announced last week that her government plans to go ahead with a consultation on changes to the country's Gender Recognition Act, allowing people to "self-certify" their gender.
Critics have warned that biological men will get the legal right to access women's hospital wards, prisons, lavatories, changing rooms and competitive sports simply by declaring they are female.