MINNEAPOLIS – Extremes in prepregnancy body mass index are linked with slower mental development, an analysis of a large, nationally representative cohort suggests.
After researchers adjusted for sociodemographics, children whose mothers were obese or underweight were 1.5-times more likely than were children of normal-weight mothers to have delayed mental development at 2 years.
No such association with body mass index (BMI) was observed for motor skills.
Dr. Stefanie Hinkle
Given the obesity epidemic, the findings have implications for pre- and inter-conception care, early intervention programs, and obesity prevention and policy, Stefanie Hinkle, Ph.D., said at the meeting.
"Focusing on obesity in children is a particular concern given they our next generation of mothers," she said at the annual meeting of the Society for Pediatric and Perinatal Epidemiologic Research.
The analysis included 6,850 children from the Early Childhood Longitudinal Study–Birth Cohort, a nationally representative sample of 3.6 million children born in 2001. At about two years of age, certified interviewers used a validated shortened version of the Bayley Scales of Infant Development II to assess mental and psychomotor development.
At 9 months postpartum, 5% of mothers reported a prepregnancy BMI categorized as underweight (less than 18.5 kg/m2); 56% normal weight (18.5-24.9 kg/m2); 25% overweight (25-29.9 kg/m2); 8% class I obese (30-34.9 kg/m2); and 6% class II & III obese (at least 35 kg/m2).
Compared with children of normal-weight mothers, mental development T scores were significantly lower for children of underweight or class II-III obese mothers. The greatest difference, a gap of 2.13 points, was observed among children of mothers with severe obesity or a BMI of 35 kg/m2 or more, said Dr. Hinkle, a postdoctoral fellow with the division of reproductive health, Centers for Disease Control and Prevention in Atlanta.
The adjusted odds for the more clinically relevant endpoint of delayed mental development, defined as at least one standard deviation below reference, were 1.48 for children of underweight moms and 1.50 for those of severely obese moms.
T scores for motor development and delayed motor development were not significantly different based on prepregnancy BMI, Dr. Hinkle said.
During a discussion at the meeting, one attendee asked whether the analysis included low birth-weight infants or took into consideration such factors as parenting styles, home environment or neighborhood environment.
"I’m just a little skeptical that obesity, all by itself, has this direct effect because there are a lot of other things that happen during child development in the first few years," said Russell Kirby, Ph.D., professor of community and family health, University of South Florida, Tampa.
Dr. Hinkle said they adjusted the models for maternal age, race/ethnicity, marital status, parity, years of schooling, smoking during pregnancy, and household poverty at the time of the assessment and for the child’s gender. Additional data were collected on factors relating to the home and will be used in a future analysis of the children at 5 years. The investigators also performed an analysis among low birth-weight infants and the findings were similar.
Session moderator Dr. Fiona Stanley, professor of pediatrics at University of Western Australia in Perth, said single-factor analyses are frustrating given that the pathways into obesity are known to be complex and involve several factors that can influence child outcomes such as maternal mental health, self-esteem and poverty.
"There are many pathways into children not doing well on Bayley scores at age 2, and maternal obesity is a marker for a pathway or set of pathways," she said in an interview. "To target just obesity is not the way forward."
Finally, an attendee pointed out that the effect of factors influencing perinatal IQ often disappears as time goes on.
The Oak Ridge (Tenn.) Institute for Science and Education sponsored the analysis. The Department of Education sponsored the Early Childhood Longitudinal Study–Birth Cohort study. Dr. Hinkle and her coauthors report no relevant conflicts of interest.