A new study by Andrea Kutinova (now Menclova-she is the nice one down this end of the corridor!) looks at the incentive effects caused by the fact that you could get out of the Vietnam draft in the US if you had family responsibilities. Andrea shows the results of the deferment on paternity timing: it turns out that the threat of being sent to war and the option to stay home if you've family responsibilities provides an incentive to speed up family formation.
The paper is "Paternity Deferments and the Timing of Births: U.S. Natality During the Vietnam War" and the abstract of the paper reads:
During the conflict in Vietnam, married men with dependents could obtain a deferment from the draft. In 1965, following President Johnson’s Executive Order 11241 and a subsequent Selective Service System announcement, the particulars of this policy changed substantially in a way which provided strong incentives for childless American couples to conceive a first-born child. This study examines the effects of the intervention on the decision to start a family. In my empirical analysis, I use data from the Vital Statistics for the period 1963–1968 and employ a difference-in-differences methodology. The estimated magnitude of the effect is substantial.Interestingly Dick Cheney's first daughter, Elizabeth, was born 9 months and 2 days after the Selective Service System announced that childless married men were to be drafted.