Women who are obese during early pregnancy have a nearly doubled risk of their child dying in the womb or soon after birth compared with non-obese women, according to a new study.

Obese women have, on average, 16 fetal deaths for every 1,000 births, compared with non-obese women who have nine fetal deaths for every 1,000 births, the study found.

However, it's important to note that fetal death is extremely rare, even among children of obese women, said study researcher Dr. Ruth Bell, clinical senior lecturer at the Institute of Health and Society at Newcastle University in England.

"The risk [of fetal death] was nearly doubled for obese women, but still quite low at 1.6 percent," Bell told MyHealthNewsDaily. Most women will give birth to a, live, healthy baby, regardless of their weight in early pregnancy, she said.

The study was published today (April 5) in the journal Human Reproduction.

Examining the risk of weight

Bell and her colleagues looked at 40,932 pregnancies that occurred between 2003 and 2005 in northern England, to see if maternal underweight (having a body mass index, or BMI, of less than 18.5), overweight (BMI of 25 to 29.9) or obesity (BMI greater than 30) increased fetal or infant death risk compared with maternal recommended weight (BMI between 18.5 and 24.9). BMI is a measure of height and weight.

Researchers found that the risk of dying in the womb or dying before a first birthday was doubled in women who were obese during pregnancy, compared with non-obese women, the study said.

However, no association between fetal or infant death was found for women who were underweight or overweight during pregnancy, the study said.

Why is obesity so dangerous?

Researchers aren't completely sure why obesity seems to be associated with an increased risk of fetal and infant death. But one possible reason is because obese women tend to have an increased risk of preeclampsia during pregnancy, which is marked by excess protein in the urine, Bell said.

Preeclampsia can stunt blood flow to the placenta, which could result in slowed growth, low birth weight and breathing problems in the baby, according to the Mayo Clinic.

Women who are obese seem to be prone to fat disturbances in the blood that could spur preeclampsia, Bell said. Obese women also tend to start pregnancy with a higher blood pressure than non-obese women, which predisposes them to preeclampsia, she added.

Therefore, it's important for obese women who are considering becoming pregnant to talk to their doctor about managing their weight, Bell said.

It's also important that pregnant women focus more on maintaining a healthy lifestyle than on losing weight during pregnancy, she said.

"The most important thing during pregnancy is to have a good quality diet to ensure both mom and baby get the nutrients they need," Bell said. "I would be concerned that a pregnant woman who tries to lose weight without proper dietary advice may be at risk of not having a healthy balanced diet."

Pass it on: Obesity during early pregnancy is associated with an increased risk of infant and fetal death, though the overall risk of the deaths is still considered extremely low.

Follow MyHealthNewsDaily staff writer Amanda Chan on Twitter @AmandaLChan.