By one means or another, Ache women successfully follow this advice and show no significant effect of the following inter-birth interval (IBI) on child mortality (Hill and Hurtado, 1996, pp. 220–221, 380–385; table 12.5), and only a small effect of the preceding interval. Many other populations show significant effects of the preceding interval on mortality and morbidity of the “index child” (Rutstein, 2005). Effects of the following interval are more difficult to study but effects on mortality and morbidity have been claimed by many. Numerous studies across the decades and continents have linked mortality of each child to IBIs, beginning with Yerusalmy (1945) (Carlaw and Vaidya, 1983; Hobcraft et al., 1985; Thapa et al., 1988). Early doubts, caused by distortions that could arise in retrospective family histories (Potter, 1977, 1988) are overcome in more recent studies that use longitudinal data, such as by Ronsmans (1996).

All over the developing world, healthcare workers and mothers are exhorted to lengthen the intervals between births in order to lower child mortality and enhance family health. A rapid series of births is suspected as a cause of “maternal depletion,” a syndrome that seems to endanger both mother and child in some populations (but not in all, Dewey and Cohen, 2007). “Weanling mortality” and morbidity, close to the time when the index child is supplanted by a new pregnancy and infant, is all too familiar in many countries (Jones et al., 2003; Lamberti et al., 2011). Reviews of recent, more statistically sophisticated studies, continue to argue for the massive worldwide effects of birth spacing on infant and child mortality and mother and child morbidity (Norton, 2005, and references therein). Effects are not restricted to the developing countries but have now been found in industrialized countries, and the type of effects expanded even into parental behavior and educational outcomes (Crowne et al., 2011).

A series of papers by Mturi and colleagues report analyses of birth spacing, fertility, and child mortality in the Tanzanian national population, using the 1991/1992 Tanzania Demographic and Health survey.