This leads to “less contraceptive use, more pregnancies, and more abortion,” said Dr Miller, a non-resident fellow at the Center for Global Development and director of the Stanford Center for International Development.
The study comes as the abortion debate hots up in the US with the Republican state of Alabama banning abortions in almost all circumstances, setting up a direct challenge to the landmark US Supreme Court ruling which gave women a constitutional right to end a pregnancy.
The authors warn their study, based on demographic and health surveys of 743,691 women and United Nations data, may underestimate the impact of the policy – also known as the Mexico City policy – because abortions are often under reported.
“The good news is, these changes are reversible,” co-author Dr Eran Bendavid, professor of medicine at Stanford University added, explaining that the analysis found that the impacts reversed after the policy was repealed between 2009 and 2014.
There have been smaller studies suggesting the policy is counterproductive but the Lancet study claims to be the largest so far and the first to show that abortion rates go down when family planning organisations are supported and contraceptives are available.