LOS ANGELES — A baby boy born in Chicago or St. Louis is about 77 percent more likely to be circumcised in a hospital in his first days of life compared with an infant born in San Francisco or Seattle, according to new data from the Centers for Disease Control and Prevention.

Nationwide, the proportion of newborn boys who are circumcised before they leave the hospital has declined nearly 10 percent since 1979, when the CDC’s National Center for Health Statistics began keeping track. In 1979, 64.5 percent of baby boys had the procedure done during their initial hospital stay; by 2010, that figure had dropped to 58.3 percent.

During that 32-year period, newborn circumcision was most popular in 1981, a year when 64.9 percent of boys had the procedure. The low point was 2007, when 55.4 percent of parents opted to circumcise their infant boys before leaving the hospital.

The national figures mask distinct regional differences, however. Generally speaking, in-hospital circumcision rates have fluctuated a bit over the last three decades but generally ended up close to where they began:

In the Northeast, 66.2 percent of newborn boys were circumcised in the hospital in 1979, as were 66.3 percent in 2010, the most recent year for which figures were available. During those 32 years, rates ranged from a high of 69.6 percent in 1994 to a low of 60.7 percent in 2007, with an average rate of 66 percent.

In the South, 55.8 percent of newborn boys were circumcised in the hospital in 1979, as were 58.4 percent in 2010. The average rate over the 32-year period was 59.4 percent, with a high of 66.1 percent in 1995 and a low of 53.8 percent in 1988.

In the Midwest, where newborn circumcision is most popular, 74.3 percent of infant boys were circumcised in the hospital in 1979, along with 71 percent in 2010. Rates ranged from a high of 82.9 percent in 1998 to a low of 68.8 percent in 2009, with an average rate of 76.8 percent.

But the story was different in the West, where two cities — San Francisco and Santa Monica, Calif. — have proposed banning the procedure altogether.