We provide estimates of impacts on maternal mortality of swings in US aid for family planning and maternal health driven by switches in implementation of the Global Gag Rule (GGR) with US Presidential Party. The GGR is a pro-life policy that prohibits aid to overseas non-governmental organisations (NGOs) if they offer abortion-related information or services (1). Since first implemented by President Reagan in 1984, it has been enacted under every Republican and revoked under every Democrat. It was tightened under President Trump and will very likely be rescinded under President Biden on January 21, 2021. Using data for 1985-2019, we demonstrate that aid for family planning has been 48% higher under Democratic presidential regimes. We estimate that a switch from Democratic to Republican party, for a country with above-median reliance on US family planning aid, is associated with an additional 0.6 deaths per 1,000 women, an increase of 8%. This erodes a fifth of the average worldwide decline in maternal mortality achieved since 1990.