How does a fetus know it’s the weekend?

Births by day of week

The chart clearly shows the trend of increased planned deliveries, such as inducement and caesarian births. Saturday and Sunday births are flat to down from 2000 to 2006, while every other day of the week has seen an increase over the same period. Also interesting is that Monday is a relatively unpopular day for delivery.

It really looks like four distinct distributions: Sunday, Monday, Saturday, and then everything else.

Data is for USA births as reported in the CDC National Vital Statistics reports, 2001 data missing.