"Women who are overweight or obese before they get pregnant are more likely to have a child who is autistic or with behavioural problems, a new review found," reports the Mail Online.
The news comes from a review that pooled the findings of 32 studies looking for a possible link between whether a woman was overweight or obese before she became pregnant, and neurodevelopmental disorders like attention deficit hyperactivity disorder (ADHD) and autism spectrum disorders (ASD) in their children.
The causes of these conditions, aside from possible genetic factors, aren't well understood.
Overall, the study found women who were overweight before they became pregnant had about a one-third increased risk of having a child with ADHD, and a 10% increased risk of having a child with autism spectrum disorders, compared with normal-weight women.
If the mothers were obese, the risks were slightly higher (two-thirds and one-third increased risk).
Although this is a useful review, it has its limitations. The findings are based on observational studies that varied widely in their studied populations, how they assessed weight status and neurodevelopmental outcomes, and the other factors taken into account.
It's possible that genetics, health, lifestyle and other family environmental factors could have played a role in the likelihood of having a child with one of these conditions.
As such, the studies aren't able to prove there's a direct link between these disorders and women who were overweight or obese before falling pregnant.
But the various risks of being overweight or obese are well established.
Obviously, not all pregnancies are planned. But if you're planning for a baby, it's recommended that the mother-to-be achieves or maintains a healthy weight before trying to conceive.
Read more about body weight and pregnancy.
The study was carried out by a team of researchers from two institutions in the US: Duke University Medical Center and Virginia Commonwealth University.
It was funded by the Eunice Kennedy Shriver National Institute of Child Health and Human Development.
The study was published in the peer-reviewed journal Pediatric Obesity.
The Mail Online article generally takes the findings at face value without recognising the limitations of this study – that is, we don't know that obesity is a causative factor of these disorders.
The story also mainly focuses on autism when in fact the study looked at several behavioural conditions, such as ADHD and cognitive and intellectual impairment.
They looked at existing evidence to investigate the association between mothers being obese or overweight before they were pregnant, and neurodevelopmental conditions such as ADHD or autism spectrum disorders in their children.
The prevalence of child behavioural and developmental conditions in western countries is rising, but the causes are poorly understood.
Antenatal exposure to environmental toxins and maternal stress and nutrition have been suggested as possible causes in previous research. This study looked at the possible link with a mother's weight.
Systematic reviews are the best way of gathering the published literature on a topic to look for a potential association between an exposure and an outcome.
The difficulty is that the findings of a systematic review are only as good as the studies the researchers include as part of their analysis.
As the studies included in this research are observational, it's difficult to account for many other factors that could have had an influence on the findings.
The researchers searched for observational studies looking at the link between a mother being obese or overweight before pregnancy and neurodevelopmental disorders in her child, including autism spectrum, ADHD, and cognitive and intellectual impairment.
They assessed the quality of these studies, looking at factors such as:
Forty-one studies met the inclusion criteria, and the findings of 32 were pooled in a meta-analysis (6 case-control studies and 26 cohort studies).
Twenty studies came from the US, with a handful from the UK, the Netherlands, Denmark, Finland, Sweden, Norway and Australia.
Pooling data from 22 cohort studies looking at being overweight, mothers who were overweight before becoming pregnant were more likely to have a child with one of the conditions being investigated (odds ratio [OR] 1.17, 95% confidence interval [CI]: 1.11 to 1.24).
From 25 cohorts that included obese women, obesity before pregnancy was associated with an even greater increase in risk of having a child with one of the conditions (OR 1.51, 95% CI: 1.35 to 1.69).
More specifically, mothers who were overweight before pregnancy were more likely than normal-weight mothers to have a child with:
There was no link between a mother being overweight and having a child with emotional or other behavioural problems.
Mothers who were obese before pregnancy were even more likely to have a child with these conditions:
The researchers concluded: "Results show that children born to mothers who are overweight or obese are at a higher risk of neurodevelopmental problems, including ADHD, ASD, greater emotional and behavioural problems, and cognitive delay."
They say that a critical next step could be to start looking at biological causes for the links, such as maternal obesity possibly influencing inflammation levels during a child's development in the womb.
This review gathered a large body of existing observational studies that investigated the association between mothers being overweight or obese before pregnancy and neurodevelopmental disorders in their children, such as ADHD.
The limitations are:
The causes of conditions such as ADHD and autism spectrum disorders remain largely unknown. But we do know that being overweight or obese has adverse health effects.
If you're planning to have a baby, taking steps to lose weight (if you're overweight) before conceiving could benefit both you and your baby, as well as reduce the risk of complications during pregnancy.
The NHS Weight Loss Plan provides information on dieting and exercise techniques that can lead to weight loss over time.