U.S. Baby Trend: More Boys Are Born Than Girls

June 15, 2005 -- It may be one of America's longest-running baby trends -- the birth of more boys than girls.

The CDC's latest records are for 2002, when newborn boys outnumbered girls by more than 94,000 infants. The trend dates back to 1940. That's before the attack on Pearl Harbor, when the baby boom generation was just a twinkle in their parents' eyes.

Every year from 1940 through 2002, an average of 91,685 more boys were born in the U.S. than girls. That adds up to a difference of more than 5.7 million boys, says the CDC.

Boy or Girl: Possible Influences

There are plenty of folk tales about what determines a baby's sex. The CDC's report doesn't get into that. But it does list some factors related to the boy-girl ratio, looking at all years combined:

• Mother's age: The ratio was lowest for women in their 40s and highest for late-teen moms.
• Child's birth order: The more babies a woman has, the more likely she is to have equal numbers of boys and girls, says the CDC.
• Mother's racial/ethnic background: Chinese women had the highest ratio of boys to girls, for all years combined. Filipino moms were a close second. The lowest ratios of boys to girls were seen in black mothers and American Indian moms.

Older fathers, lower maternal weight, stress, and environmental toxins may also lower the ratio, says the CDC, which didn't track those factors. Data came from birth certificates in all 50 states and Washington, D.C.

Trends Over Time

The boy-girl ratio peaked in 1946. Back then, there were 1,059 boys born per 1,000 girls. The lowest ratio -- 1,046 males per 1,000 female births -- was seen twice, in 1991 and 2001.

There have been hills and valleys along the way. Significant trends in the ratio were a drop from 1942 to -1959, a rise from 1959 to 1971, and another drop from 1971 to 2002, says the CDC.

SOURCES: CDC: "Trend Analysis of the Sex Ratio at Birth in the United States." News release, CDC.