Vice president Mike Pence, a Republican and longtime hero of the anti-abortion movement, is due to be the most senior government official ever to speak in person at the rally, organisers said. Photograph: (Reuters)
The march comes days after Washington was flooded by hundreds of thousands of anti-Trump protesters, many of them were backers of abortion
Anti-abortion activists gathered in Washington on Friday for the 44th March for Life, buoyed by President Donald Trump's pledge to restrict the procedure and Vice President Mike Pence's plan to address the marchers.
Organisers expect tens of thousands of supporters to converge on the National Mall for the march, which is held each year close to the anniversary of the US Supreme Court's Roe v Wade ruling that legalised abortion in 1973.
Vice President Mike Pence, a Republican and longtime hero of the anti-abortion movement, is due to be the most senior government official ever to speak in person at the rally, organisers said. As governor of Indiana, Pence signed what were seen as some of the nation's strictest abortion laws.
Senior Trump aide Kellyanne Conway, New York Cardinal Timothy Dolan and several Republican lawmakers also are scheduled to speak.
Rally participants will march from the Mall about 1.5 miles (2 km) to the Supreme Court.
The March for Life comes six days after Washington was flooded by hundreds of thousands of anti-Trump protesters, many of them backers of abortion rights. That protest came a day after Trump was sworn in as president.
Trump has said Roe v Wade should be overturned and has vowed to appoint an anti-abortion justice to fill the Supreme Court seat left vacant by the death of Justice Antonin Scalia last year.
He also has pledged to defund Planned Parenthood, which draws the ire of many Republicans because it provides abortions, along with other services.
In a speech to Republican lawmakers at a retreat in Philadelphia on Thursday, Trump noted that on Monday he reinstated a national policy banning US aid to non-governmental organisations abroad that provide or "promote" abortion.
Trump, who has frequently accused the media of underestimating the crowd at his inauguration, predicted the size of the march crowd would be "300, 400, 500, 600,000 people."
The rally comes as the number of US abortions has fallen to a record low. The Guttmacher Institute, a reproductive health and rights organisation, said last week that it dropped below 1 million in 2013 for the first time since 1975.
The drop could be because of improved contraceptive practices as well as restrictive abortion laws, the institute said.
A Pew poll last year showed 57 per cent of Americans believe abortion should be legal in all or most cases.