Women who are obese before they become pregnant may be at increased risk of having a baby with defects of the brain and spinal cord, especially if they tend to put on weight around the waist, according to new research from the March of Dimes.
But a woman's body mass index (BMI) before pregnancy had no relationship to her likelihood of having a child with certain types of heart malformation, Drs. Gary M. Shaw and Susan Carmichael of the Children's Hospital Oakland Research Institute in California found.
Previous studies have linked maternal obesity to a number of birth defects, especially neural tube defects, which are malformations of the brain and spinal cord, Shaw and Carmichael note in the journal Epidemiology. The most common neural tube defects are spina bifida, in which the spinal cord fails to close completely during foetal development, and anencephaly, in which part or all of the brain doesn't develop.
To examine the relationship between obesity and other weight-related factors in the risk of these and other birth defects, the researchers looked at 700 women who gave birth to healthy children and 659 who delivered babies with spina bifida, anencephaly, a type of heart malformation called transposition of great arteries, or a different heart defect known as tetralogy of Fallot.
There was no association with prepregnancy BMI and either heart defect. Women with BMIs of 30 or greater were 60 percent more likely to have a child with anencephaly and 40 percent more likely to have a baby with spina bifida than their slimmer peers. But babies born to mothers who said that they had gained weight around their waists rather than their hips were 2,4 times as likely to have anencephaly and at 1,8 fold greater risk of spina bifida.
Abdominal weight gain may play a role in the development of type 2 diabetes, the researchers note. "Thus, this finding may offer a clue to underlying mechanisms for the associations of obesity with birth defect risk, given that clinical diabetes is also a risk factor for birth defects," they write.