Atlanta ? U.S. infant mortality has climbed for the first time in more than four decades, in part because older women are putting off motherhood and then having multiple babies via fertility drugs, the government said Wednesday.

At the same time, U.S. life expectancy reached an all-time high of 77.4 years in 2002, the Centers for Disease Control and Prevention said. Life expectancy in 2001 was 77.2 years.

The infant mortality rate rose from 6.8 deaths per 1,000 live births in 2001 to 7.0 deaths per 1,000 in 2002. The last time the rate rose was in 1958.

“We were surprised because it has been declining fairly steadily for more than four decades,” said Joyce Martin, lead statistician for the CDC. “You’re always concerned when an important indicator in public health increases.”

The 2002 rise may be a one-time blip, since the U.S. rate for 2003 is expected to drop, a preliminary review by the CDC indicates.

CDC officials said the exact reasons for the increase were not yet clear. But previous CDC research suggests the rise in infant mortality may reflect the long trend among American women toward delaying motherhood.

Women who put off motherhood until their 30s or 40s are more likely to have babies with birth defects or other potentially deadly complications.

Also, older women are more likely to use fertility drugs to get pregnant, and such drugs often lead to twins, triplets and other multiple births. And multiple births carry a higher risk of premature labor and low birthweight — conditions that can endanger babies’ lives.

CDC officials said other factors might have also led to the rise in infant mortality. For example, more babies are being born prematurely or at low birthweights because more doctors are inducing labor and using Caesarean sections for delivery, the CDC said.

The number of multiple births and other high-risk pregnancies in the United States steadily increased in the past decade as more women have put off having their first child. Recent birth rates for women ages 35 to 44 were the highest levels for those age groups in three decades, the CDC reported in September.

More than half of the multiple births in 2002 were born preterm or had low birthweight, the CDC said.