It is estimated that only 23 of the 75 most needy countries are on track to achieve a two-thirds reduction in under-5s mortality between 1990 and 2015 (Millennium Development Goal (MDG) 4). Despite this, one of the world's poorest countries (Niger) has had remarkable success (Agbessi Amouzou and colleagues. Lancet 2012;380:1169–78; see also comment, ibid: 1127–8). How has this been achieved?

Niger is ranked 186 out of 187 countries on the Human Development Index. The average woman there will have seven children …