"We can see fat sequestered in the placentas of obese mothers when it should be going to the baby to support its growth," Yuan-Xiang Pan, a professor of nutrition at the University of Illinois, said in a statement. "The nutrient supply region in the placenta of an obese mother is half the size of that of a normal-weight mother, even when both are eating the same healthy diet."
Pan blames what he calls the obesogenic environment of the mother, which includes increased triglycerides, high levels of the hormone leptin and elevated amounts of non-esterified fatty acids circulating in the obese expectant mother's body.
Triglyceride and non-esterified fatty acids levels are nearly twice as high in obese mothers, even when they consume healthy diets during pregnancy, Pan found.
"My advice is, lose weight well before you become pregnant," Pan recommended.
In the study, Pan and colleagues compared the placentas of obese rats fed a healthy diet throughout their pregnancies with the placentas of obesity-resistant rats fed the same diet.
"Although the obese females didn't gain much weight on the healthy diet, the obesogenic environment remained, and it affected nutrient transport regulation in the placenta," Pan said.
The study published in the journal Biology of Reproduction found obese mothers gave birth to babies that were up to 17 percent smaller than they should have been and their infants may have lifelong increased risk of disease as result.