Pregnancy Weight Gain May Influence Autism Risk

Megan Brooks

October 31, 2013

The amount of weight a woman gains while pregnant may influence her risk of having a child with autism, a retrospective study suggests. However, researchers urge caution in interpreting the finding.

In 2 separate cohorts from Utah, researchers found a positive association between prenatal weight gain, but not prepregnancy weight, and risk for autism spectrum disorder (ASD).

Pregnancy weight gain "may serve as an important marker of autism's underlying gestational etiology," the researchers write.

But lead investigator Deborah A. Bilder, MD, from the University of Utah in Salt Lake City, cautioned that women should not try to limit weight gain during pregnancy on the basis of this study.

Doctors should reassure their patients that "this study was not designed to identify a cause-and-effect relationship but rather to look for an association which likely reflects a shared etiology," she told Medscape Medical News. "As such, these results do not change the current, well-established guidelines that are in place for the recommended amounts of weight gain for a healthy pregnancy," Dr. Bilder added.

The study was published online October 28 in Pediatrics.

Hormone Dysregulation?

As previously reported by Medscape Medical News, prior studies have suggested links between maternal body mass index (BMI) and gestational weight gain and ASD risk, but confounding factors potentially shared by ASD and obesity, such as obstetric complications, parity, advanced maternal age, and socioeconomic status, may have played a role.

This new study found an association between ASD risk and prenatal weight gain but not prepregnancy BMI, after accounting for important confounding variables.

In a cohort of 128 children diagnosed with ASD and a matched control group of 10,920 children, ASD risk was significantly associated with pregnancy weight gain. For each 5 pounds of weight gained, the adjusted odds ratio (aOR) was 1.10 (95% confidence interval [CI], 1.03 - 1.17).

A second sample of 288 children with ASD and 493 unaffected siblings revealed similar findings (aOR for each 5 pounds gained, 1.17; 95% CI, 1.01 - 1.35). Prepregnancy BMI was not associated with ASD in either cohort.

These 2 cohorts demonstrated "remarkably similar findings particularly in light of their differences in case ascertainment methods, control group selection, and participant demographics," the researchers note.

They add, however, that the absolute difference in pregnancy weight gain between case and control groups (about 3 pounds) is "considered clinically insignificant in current obstetrical practice."

"The mechanism that we hypothesized when we designed this study was that in utero steroid hormone dysregulation may contribute to the development of autism," said Dr. Bilder.

"The mother, child, and placenta collectively create the steroid environment of the fetus. Prepregnancy BMI and pregnancy weight were selected as easily accessible markers of this endocrine environment because they have been used as such in studies focusing on other disease states, like cancer.

"This study did not prove that steroid hormone dysregulation causes autism, but provides support to this hypothesis and suggests the need to look for direct evidence of this phenomenon," she added.

Not Causal

Reached for comment on the study, Max Wiznitzer, MD, associate professor of pediatrics and neurology at Case Western Reserve University and pediatric neurologist at Rainbow Babies and Children's Hospital in Cleveland, Ohio, said that the authors were "careful to state that they found an association but not a causal association; it is likely a marker of some other risk factor rather than the actual reason."

Dr. Wiznitzer, who was not involved in the study, noted that the odds ratios of 1.10 and 1.17 reflect a "very modest increase in the risk that is a small absolute number." The difference in weight gain between the 2 groups is "just 3 pounds (9% to 10% of the total weight gain). This is a small number that can be influenced by the type of scale, time of day of the weight measurement, hydration status, etc," he said.

"The bottom line ― I do not think that, by itself, this is a clinically significant finding that has identified a major risk factor for ASD. Rather, it is a minor finding that has to be considered in the context of other pregnancy-related factors that may influence the occurrence of ASD. We have to be careful not to ascribe a cause-effect relationship to every little finding in this population," Dr. Wiznitzer concluded.

The study was partially funded by the Centers for Disease Control and Prevention, the Utah Registry of Autism and Developmental Disabilities, the National Institutes of Health, and Autism Speaks. The authors and Dr. Wiznitzer have disclosed no relevant financial relationships.

Pediatrics. Published online October 28, 2013. Abstract

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