ATLANTA (AP) – U.S. women are dying from childbirth at the highest rate in decades, new government figures show. Though the risk of death is very small, experts believe increasing maternal obesity and a jump in Caesarean sections are partly to blame.

Some numbers crunchers note that a change in how such deaths are reported may be a factor.

“Those of us who look at this a lot say it’s probably a little bit of both,” said Dr. Jeffrey King, who led a recent New York review of maternal deaths.

The U.S. maternal mortality rate rose to 13 deaths per 100,000 live births in 2004, according to statistics released this week by the National Center for Health Statistics. The rate was 12 per 100,000 live births in 2003 – the first time the maternal death rate rose above 10 since 1977.

To be sure, death from childbirth remains fairly rare in the United States. The death of infants is much more common – the nation’s infant mortality rate was 679 per 100,000 live births in 2004.

But the fact that maternal deaths are rising at all is shocking, said Tim Davis, a Virginia man whose wife Elizabeth died after childbirth in 2000.

“The hardest thing to understand is how in this day and age, in a modern hospital with doctors and nurses, that somebody can just die like that,” he said.

Some health statisticians note the total number of maternal deaths – fewer than 600 each year – is small. It’s so small that 50 to 100 more could raise the rate, said Donna Hoyert, a health scientist with the National Center for Health Statistics. The rate is the number of deaths per 100,000 live births.

In 2003, there was a change in death certificate questions in the nation’s most populous state, California. That may have resulted in more deaths being linked to childbirth.

Some researchers point to the rising C-section rate, now 29 percent of all births – far higher than what experts say is appropriate. Like other surgeries, Caesareans come with risks related to anesthesia, infections and blood clots.

Experts also say obesity may be a factor. Heavier women are more prone to diabetes and other complications, and they may have excess tissue and larger babies that make a vaginal delivery more problematic. That can lead to more C-sections. “It becomes this sort of snowball effect,” said King, who is medical director of maternal-fetal medicine at Riverside Methodist Hospital in Columbus, Ohio.

The age of mothers could be a factor, too. More women are giving birth in their late 30s and 40s, when risks are greater.

Sometimes, there is no clear explanation for a woman’s death. Tim Davis’ 37-year-old wife, Elizabeth, died a day after a vaginal delivery at a Danville, Va., hospital in September 2000.

She had a heart attack after a massive blood loss, Davis said. It’s not clearly known what caused the heavy bleeding. There was no autopsy, he said, a decision he now regrets.Two previous births had gone well.

“Nothing led us to believe anything was wrong with this pregnancy. She was like a picture of health,” he continued, noting she had been a YMCA fitness instructor.

A lawsuit against the hospital ended in a settlement. Davis also sued the obstetrician, but a jury ruled in the doctor’s favor.

The child born that day, Ethan, starts second grade next week. “He’s a happy kid,” Davis said. “He’s just never had a mom.”