Hispanic women are almost twice as likely to die from complications of pregnancy as white women, according to the first national look at maternal mortality.

But despite similar levels of poverty and prenatal care, they are less likely to die from pregnancy than black women, the new study says. The difference, researchers say, is a medical mystery that needs to be investigated further.

"We expected Hispanic women to fare worse than non-Hispanic white women, but we found the disparity in the risk of pregnancy-related death between black and Hispanic women striking," researchers from the U.S. Centers for Disease Control and Prevention (CDC) reported last week in the journal Obstetrics & Gynecology.

The researchers reported earlier this year that black women are about four times as likely to die from pregnancy or delivery complications as white women.

Pregnancy is rarely fatal for U.S. women. During the 14 years studied, 3,777 women died, with 623 of those deaths among Hispanic women. The most common cause of death is extremely high blood pressure, the origin of which isn't well understood. Death can also occur from hemorrhage, blood clots or other conditions. The researchers counted pregnancy-related deaths that occurred up to one year after delivery.

The study found that about six of every 100,000 non-Hispanic white women who give birth die. For Hispanic women, the figure is about 10 deaths per 100,000; for black women it is 25 deaths per 100,000.

Although the numbers seem small, researcher Lisa Koonin said, the death of a young mother sends shock waves that cannot be described by statistics.

"This is a profound tragedy for a family, and for a community," said Koonin, who was on the CDC team.

The loss is even more profound because it is usually preventable if a woman is under a doctor's care, said Gary Cunningham, chairman of obstetrics and gynecology at the University of Texas Southwestern Medical Center at Dallas.

"It's one of the prime indicators of the health care system of any given country," he said.

The health of Hispanic women and children is also of increasing importance nationally: In 1996, Hispanic women accounted for 18 percent of deliveries, but only 11 percent of women of childbearing age, the CDC says.

To examine maternal mortality, the CDC researchers pulled data from death certificates and birth certificates in all states from 1979 through 1992. Until recently, a study like this wasn't possible because the records were not detailed enough. Since deaths of this kind are so infrequent, researchers have must have large pools of numbers before any trends reveal themselves.

"You can't really determine much from one year, one state," Koonin said. "This is actually the first time we've been able to do this. There's been really a dearth of information on Hispanic women."

Researchers expected the difference in death rates between Hispanic and non-Hispanic women because of Hispanics' higher levels of poverty--a factor that makes women less likely to obtain early prenatal care.

"Those of us who deal with indigent patients say it's certainly no surprise," said Cunningham.

But the differences between Hispanic and black women are harder to explain. Both groups have similar levels of prenatal care and similar economic status, the authors state: In 1996, 60 percent of Hispanics and 55 percent of blacks lived in families considered poor or nearly poor, compared with only 26 percent of whites.

"I think that it really shows us that socioeconomics isn't everything," said Peter Norton, former chairman of a Texas Medical Association committee examining maternal mortality.

The study didn't address the reasons behind the numbers. Some experts suspect that cultural differences may account for the distinctions between Hispanic and black women despite similar levels of poverty.

However, Ken Leveno, a physician at Parkland Memorial Hospital in Dallas who has studied racial differences in infant mortality, said he believes that poverty is the overriding reason for the findings.

"A woman is a woman is a woman, as far as I'm concerned," he said, adding that historically, maternal mortality rates have been difficult to gauge because deaths are underreported in certain groups. The study's authors point out that their data probably missed more than half the deaths.

"If you're poor, you have worse health outcomes," he said, "I don't care who you are."

In addition to economics, known influences on maternal health include the woman's age and the number of children she has. How these play into the Hispanic figures is unclear.

"This generates questions rather than provides answers," Koonin said of the research.

She said scientists at the CDC and elsewhere will look for some of those answers.

"We need to move further into research into how to prevent problems from happening," Koonin said. "There are still disparities among women. We have not reduced pregnancy-related mortality to its lowest possible rate."