Children can be expensive, and it appears that the American public has taken notice; birth rates have dropped significantly since 2007, when the economic downturn began. According to the Pew Research Center, the number of births per 1,000 women age 15-44 fell from 69.6 in 2007 to an estimated 64.7 in 2010.

[See slideshows of cities with the highest and lowest birth rates.]

According to data from the U.S. Census Bureau's American Community Survey, more women in the western United States are having children, while the East and Northeast have lower birth rates. Indeed, cities in the western United States are well-represented among the metropolitan areas with the highest birth rates, as measured by the number of women of childbearing age who had births in 2010. Three metropolitan areas in Utah, as well as three in California and one in Nevada, are among those with the highest rates in the country, according to census estimates.

Some of the trends can be explained by demographics, such as age.

Utah has the lowest median age of any state in the country, at 29.2. The American Community Survey's data takes into account women age 15 to 50 who had births in the last year, which is a broad age range in terms of childbearing. "Age structure, even within 15 to 50, can definitely affect the rate," says Carl Haub, senior demographer at the Population Reference Bureau. "Women 40 and over don't have very many children," he says, meaning that states with many younger people, like Utah, are more likely to have higher birth rates (and all of those new children pull the median age downward even more). Meanwhile, several states in the Northeast, like Maine, Pennsylvania, and Connecticut, are among the states with the highest median ages. Some larger cities there are among those with the lowest birth rates.

Haub also says that religion could contribute to Utah's high fertility; the state has the highest share of Mormons in the United States, and the Mormon religion has traditionally been associated with large families.

Race and ethnicity also are strongly linked to birth patterns. "Typically in a population where you see more African-Americans and Latinos, they tend to have children at younger ages and then that will increase the birth rate that way," says Zhenchao Qian, professor of sociology at Ohio State University. Starting to have kids at an early age means a longer window for childbearing, which can mean more children. Several cities with high concentrations of these minorities are among the cities with the highest birth rates: McAllen, Texas, has a large Hispanic population, and Memphis, Tenn., has a high concentration of African-Americans.

Likewise, education and fertility are inversely related; more educated populations tend to delay childbearing in favor of school. For example, for many highly educated people, the ages of 18 to 22 are devoted to college, not starting a family. "Highly educated people, they get out of college, they have jobs, and then they have families. So the timing is being pushed. ... They're likely to have children at later ages," says Qian, meaning a smaller window for having children and therefore potentially smaller families. The Northeast tends to have more college- and advanced-degree holders than the rest of the country, which may also account for lower fertility rates in many northeastern cities.

Of the 103 U.S. metropolitan areas with populations of 500,000 or greater, these are the 11 with the highest rates of women age 15 to 50 with births in 2010.

Metropolitan Area Women 15-50 with births (per 1,000) Margin of Error

1. Memphis, Tenn.-Miss.-Ark. 107 10

2. Ogden-Clearfield, Utah 90 13

3. Provo-Orem, Utah 85 12

4. McAllen-Edinburg-Mission, Texas 80 12

5. Stockton, Calif. 74 9

6. Salt Lake City, Utah 71 8

7. Bakersfield-Delano, Calif. 69 10

8. Omaha-Council Bluffs, Neb.-Iowa 67 9

9. Fresno, Calif. 66 11

10 (tie). Houston-Sugar Land-Baytown, Texas 65 4

10 (tie). Las Vegas-Paradise, Nev. 65 7