Pregnant women who are obese or overweight may have an increased risk of miscarriage, stillborn or infant death, according to a recent study CNN reported.

Researchers found that high maternal body mass index before or in early pregnancy is associated with an increased risk of delivering a stillborn baby, CNN reported.   Women who are severely obese - with a body mass index over 40 - are two to three times more likely to experience complications.

"We found weak, but statistically significant increases in risk even within what is considered the normal ranges of BMI," lead study author Dagfinn Aune told CNN News. "For example, the relative risk of stillbirth, perinatal and infant death increased by 20 percent, 11 percent and 10 percent already at a BMI of 25 compared with a BMI of 20, however, the really strong associations were observed among women who were either obese or severely obese who had up to two- to three-fold increases in the risk compared to lean women."

The findings were based on a review of previously published studies.

For the study, researchers looked at 38 studies to better understand the potential risks to an unborn child in relation to its mother's body mass index. The studies included data from more than 10,147 fetal deaths, more than 16,274 stillbirths, more than 4,311 perinatal deaths, 11,294 neonatal deaths, and 4,983 infant deaths.

Researchers found that even modest increases in maternal body mass index were associated with increased risk of fetal death, stillbirth, neonatal death, perinatal death, and infant death.

The study authors suggest that several biological mechanisms could explain the association found in this study, including that being overweight or obese has been associated with increased risk of preeclampsia, gestational diabetes, type 2 diabetes, gestational hypertension, and congenital anomalies, conditions that have been strongly associated with risk of fetal and infant death. "... further studies are needed to investigate the mechanisms involved."

"Weight management guidelines for women who plan pregnancies should take these findings into consideration to reduce the burden of fetal deaths, stillbirths, and infant deaths," researchers said in the study.

The findings were recently published in JAMA.