The United States Centers for Disease Control and Prevention has kept statistics that say that most babies are born during the summer, and there is a birth peak in August. The latest year for which these statistics are available is 2006. That year, August had the most US births, just like in 10 out of the 16 previous years. CDC estimated that almost nine percent of births occurred then, while February had the least.
People like Paul Sutton, a CDC health statistics demographer, believe that weather conditions have a very important part in all this. He says that as temperatures drop in the late fall and in winter, people tend to spend more time indoor and have more chances of heating up things at home. The result comes some nine months later, under the shape of a new born baby.
According to the same statistics, the most common day of the week for baby deliveries in the United States in 2006, was Wednesday. That year, Tuesday lost its number one place, that it had occupied since 1990.
T.J. Mathews, a demographer at the CDC's National Center for Health Statistics, said that in other years, July or September had the highest births number. Every year, from 1990 to 2006, August had the most births every year, except for six years, when July took over: 1992, 1993, 1997, 1998, 2003 and 2004, according to National Center for Health Statistics.
Usually, late summer months see an increase in the number of newborns. “It must have something to do with the time of conception and whether there are timing issues with the outcome of pregnancy, besides just a live birth,” Mathews told LifesLittleMysteries.
Worldwide birthing statistics depend on climate and cultural factors, as this influences the time on conception. In Japan for example, a study conducted by the University of Occupational and Environmental Health in Kitakyushu City, noted that the country has two peaks in birth rates during the year: from December to February, and in August and September.
Scientists think that it must be the popularity of springtime marriages in Japan and the seasonal temperature variations that cause these peaks.