Lower infant mortality and access to contraception reduce fertility in low- and middle-income nations

Although average contraceptive use has increased globally in recent decades, an estimated 222 million (26%) of women of child-bearing age worldwide face an unmet need for family planning -- defined as a discrepancy between fertility preferences and contraception practice, or failing to translate desires to avoid pregnancy into preventative behaviours and practices. While many studies have reported relationships between availability of contraception, infant mortality, and fertility, these relationships have not been evaluated quantitatively across a broad range of low- and middle-income countries. Using publicly available data from 46 low- and middle-income countries, we collated test and control variables in six themes: (i) availability of family planning, (ii) quality of family planning, (iii) maternal education, (iv) religion, (v) mortality, and (vi) socio-economic conditions. We predicted that higher nation-level availability/quality of family-planning services, maternal education, and wealth reduce average fertility, whereas higher infant mortality and religious adherence increase it. Given the sample size, we first constructed general linear models to test for relationships between fertility and the variables from each theme, from which we retained those with the highest explanatory power within a final general linear model set to determine the partial correlation of dominant test variables. We also applied boosted regression trees, generalised least-squares models, and a generalised linear mixed-effects models to account for non-linearity and spatial autocorrelation. On average among all countries, we found an association between all main variables and fertility, with reduced infant mortality having the strongest relationship with reduced fertility. Access to contraception was the next-highest correlate with reduced fertility, with female secondary education, home health visitations, and adherence to Catholicism having weak, if any, explanatory power. Our models suggest that decreasing infant mortality and increasing access to contraception will have the greatest effect on decreasing global fertility. We thus provide new evidence that progressing the United Nations Sustainable Development Goals for reducing infant mortality can be accelerated by increasing access to any form of family planning.