Shamma Alam and I just finished a paper on the effects of income shocks on the timing of fertility in Tanzania using the Kagera data set. There are significant reductions in the likelihoods of being pregnant and giving birth following shocks, consistent with prior results in the literature. What is new is that we can show that this is predominately the results of an increased use of contraceptives. This is interesting for two reasons. First, it shows that the postponement of fertility following a shock is the result of an conscious decision, rather than being an unintended consequence of the shocks' effect on, for example, health or migration. Second, the postponement is achieved almost entirely through the use of traditional contraceptives. This shows that, once the incentives are strong enough, people are able to control their fertility even in the absence of modern contraceptives. The full abstract is:

This paper examines the relationship between household income shocks and fertility decisions. Using panel data from Tanzania, we estimate the impact of agricultural shocks on pregnancy, births, and contraception use. We estimate individual level fixed effect models to account for potential correlation between unobservable household characteristics and both shocks and decisions on fertility and contraceptive use. The likelihood of pregnancies and childbirth are significantly lower for households that experience a crop shock. Furthermore, women significantly increase their contraception use in response to crop losses. We find little evidence that the response to crop loss depends on education or wealth levels. The increase in contraceptive use comes almost entirely from traditional contraceptive methods, such as abstinence, withdrawal, and the rhythm method. We argue that these changes in behavior are the result of deliberate decisions of the households rather than the shocks' effects on other factors that influence fertility, such as women’s health status, the absence or migration of a spouse, the dissolution of partnerships, or the number of hours worked. We also show that, although traditional contraceptives have low overall efficacy, households with a strong incentive to postpone fertility are very effective at using them.