LOS ANGELES - Pregnant women who eat high-fat diet may be more likely to have a higher rate of stillbirth, a new study suggests.

Researchers at Oregon Health & Science University (OHSH) came to the conclusion after observing 24 pregnant Japanese macaques that ate either a diet comprising 32 percent calories from fat or a control diet with 14 percent fat calories for at least four years.

The researchers found the monkeys that ate a high-fat diet experienced a significant decrease in blood flow from the uterus to the placenta, a reduction of 38 percent to 56 percent, and a rise in placental inflammation.

This was the case regardless of whether the monkeys were obese or slender. The risk of stillbirth was further compounded, however, when the monkeys were obese with hyper-insulinemia, or pre-diabetes.

Eating a high-fat diet decreases blood flow from the mother to the placenta, the temporary organ that nourishes the unborn fetus, thus raising the risk of stillbirth, the researchers explained.

Because the placental structure of the Japanese macaque is very similar to that in humans, cause and effect can be better established, the researchers said.

Additional studies are needed to determine exactly how a high- fat diet decreases placental blood flow, the researchers noted.

This is the first study to explain exactly how a fatty diet contributes to stillbirth, the researchers said in the study appearing in the June edition of the journal Endocrinology.

The researchers hope their work will inform expectant moms and their physicians about the inherent dangers of a high-calorie, high- fat diet.

"This study demonstrates that maternal diet during pregnancy has a profound influence on both placental and fetal development," said Antonio Frias, M.D., principal investigator and assistant professor of obstetrics and gynecology (perinatology/maternal-fetal medicine) in the OHSU School of Medicine.

"The high-calorie, high-fat diet common in our society has negative effects on placental function and may be a significant contributor to adverse pregnancy outcomes, such as stillbirth."

Previous studies have shown that nearly all adverse outcomes during pregnancy -- abnormal fetal growth, preeclampsia, preterm labor and stillbirth -- are in some way associated with an abnormally developed, or damaged, placenta, the temporary organ that nourishes the unborn fetus.

In addition, maternal obesity has been associated with placental inflammation and dysfunction and an increased risk of stillbirth.

Taking these findings into account, the researchers hypothesized that eating a diet high in fat during pregnancy also may increase the risk of placental inflammation and the risk of stillbirth.

The researchers said they plan to conduct further studies on the impact of dietary changes and diet supplementation on improving outcomes in both monkeys and humans.