Maternal obesity before pregnancy significantly increases the risk for offspring with anorectal atresia, hypospadias, limb reduction defects, diaphragmatic hernia, and omphalocele, researchers reported.
D. Kim Waller, Ph.D., of the University of Texas School of Public Health, Houston, and her associates used data from the National Birth Defects Prevention Study to assess whether maternal weight affected risk for several categories of structural birth defects. This is the first study to report a link between maternal obesity and these five types of defects using sufficient sample sizes of 150 or more cases.
More than half of American women aged 20–39 years are estimated to be overweight (with a body mass index [kg/m
However, “the potential relation between obesity and other birth defects remains less certain, as those studies that have examined a range of different birth defects did not have sufficient numbers of cases to generate precise odds ratios,” the researchers said.
The National Birth Defects Prevention Study not only has a very large sample size but also includes “well-defined, state-of-the-art procedures for case definition, clinical review, and classification of birth defects—which are often complex and difficult to classify…. [F]or many types of birth defects, it provides much greater statistical precision than has been previously possible,” they noted.
The investigators analyzed data on 10,249 babies born with structural birth defects in eight states between 1997 and 2002, as well as 4,065 control subjects representative of the general population.
Maternal obesity was found to raise the risk for spina bifida and heart defects, confirming the findings of previous studies. It also significantly increased the risk for anorectal atresia, hypospadias, limb reduction defects, diaphragmatic hernia, and omphalocele, with odds ratios ranging from 1.3 to 1.6.
Maternal obesity also carried a borderline increase in risk for cleft palate, the researchers said (Arch. Pediatr. Adolesc. Med. 2007;161:745–50).
Maternal overweight significantly increased the risk for heart defects, hypospadias, and omphalocele, and slightly raised the risk for craniosynostosis.
In contrast, “mothers who were underweight had no significant increase or decrease in risk for these birth defects, except for a modest increase in risk for cleft lip with or without cleft palate,” Dr. Waller and her associates said.
Unlike previous studies, this analysis failed to demonstrate an association between maternal obesity and anencephaly, hydrocephaly, or cleft lip. However, this result may have been to the result of chance, because the number of cases of these three birth defects was relatively low.
The reason that maternal obesity or overweight is associated with birth defects is unknown.
Because an excess of these same defects has been reported in women with diabetes who become pregnant, it is possible that alterations in glycemic control underlie the association, the investigators added.