By using birth certificates for Chile and Spain we investigate differences in mother and child
characteristics according to season of birth. Our findings reveal that children born in winter are more
likely to have a mother who is a teenager and unmarried at date of birth. Spanish data also reveals that
women giving birth in winter are more likely to be out of the labor force, a result largely driven by high
skilled mothers. We additionally find that children born in the winter months have fewer weeks of
gestation, lower birth weights and smaller size. Finally for Spain, the 2001 population census and the
1999 fertility survey confirm the seasonal pattern in mother characteristics, and indicate that it is
mostly driven by women who planned the births.