In a comment on my blog about the Distribution of Birth Dates, Mary O'Keeffe sent a link to an article that addressed several questions about the distribution of births, including how tax incentives had changed births around the end of the year.
"Here is an abstract from a paper published in the Journal of Political Economy which attempted to measure the size of the tax incentive effect on behavior.
Because the tax savings of having a child are realized only if the birth takes place before midnight, January 1, the incentives for the "marginal" birth are substantial. Using a sample of children from the National Longitudinal Survey of Youth, we find that the probability that a child is born in the last week of December, rather than the first week of January, is positively correlated with tax benefits. We estimate that increasing the tax benefit of having a child by $500 raises the probability of having the child in the last week of December by 26.9 percent."
The article had several nice graphs and tables. Here are a couple of graphs that I found pertinent:
This chart shows the births in the last week before new years (Black) and the following first week in January for consecutive year. You can click on the chart to enlarge.
It also had a graph which supported my belief that weekend births had become far less likely with the practice of inducing labor. Here is that one: