The study, by researchers at the University of Texas led by D. Kim Waller, Ph.D., was conducted on 10,249 women in eight states whose babies were born with birth defects between 1997 and 2002.
The women were contacted between six weeks and 24 months after the baby's birth and asked for their height and weight before pregnancy, along with other demographic and medical information. These women were compared with 4,065 women who had babies without birth defects during the same time period.
The researchers noted that mothers of babies with the following seven of 16 birth defects were more likely to be obese than mothers of infants without birth defects.
Some of these defects seen in the babies were:
· Spina bifida, a condition that occurs when part of the spinal cord is uncovered, causing incontinence and problems with mobility
· Anorectal atresia, malformation of the anal opening
· Hypospadias, which occurs when the urethra opens on the underside instead of the end of the penis.
· Limb reduction defects, such as small or missing toes, fingers, arms or legs
· Diaphragmatic hernia, or an opening in the diaphragm that allows abdominal organs to move into the chest cavity and may cause lungs to be underdeveloped
· Omphalocele, in which the intestines or other abdominal organs protrude out through the navel
Though the researchers are still not sure why obesity seems to cause birth defects, they say that it might be due to the alterations in glycemic control.
"The reasons for an association between maternal obesity and a spectrum of structural birth defects are unknown. Both animal studies and human studies provide substantial evidence that alterations in glycemic control are responsible for an increased risk of a range of structural birth defects among women who have diabetes prior to becoming pregnant," the authors write.
"Thus, a similar mechanism to that occurring in women with diabetes may be responsible for the associations observed between maternal obesity and specific categories of birth defects," they added.
"Our study supports previous evidence as well as provides new evidence for the associations between maternal obesity and particular categories of birth defects. Future inquiries are needed to unravel the underlying reasons for these associations," the authors conclude.
The study is published in the August issue of Archives of Pediatrics & Adolescent Medicine, one of the JAMA/Archives journals.