A large systematic review has also found increased risk of ADHD and other problems that weight management may mitigate.
Excess weight before and during pregnancy heightens the risk of neuropsychiatric problems including autism spectrum disorder and ADHD, according to a meta-analysis of more than 40 studies including nearly 3.7 million mother-child pairs.
In the most striking finding, children whose mothers were obese during their pregnancy had more than twice the risk of ASD compared with those whose mothers were in the normal range.
The study, published in Psychiatry Research, set out to find links between a range of conditions and overweight and maternal overweight and obesity both preconception and during pregnancy.
Sixteen studies looked at ADHD, and the meta-analysis found 18% and 57% increased risk with exposure to preconception overweight and obesity, respectively, and 19% and 32% increased risks with overweight and obesity during pregnancy.
With ASD, which seven studies investigated, the increased risks with preconception overweight and obesity were 9% and 42%, while for overweight and obesity during pregnancy they were 24% and 223% (more than double).
Positive associations were also found for conduct disorder, psychotic disorder, externalising behaviours and peer relationship problems.
None were found for children’s mood, anxiety, personality, eating and sleep disorders or prosocial problems.
The mechanisms behind these associations are not fully understood, the authors say, but they cite several plausible options.
Direct effects could include chronic low-grade inflammation, oxidative stress, dysregulated fatty acid metabolism and hormonal imbalances changing the intrauterine environment and disrupting fetal brain development.
Child mental health could also be mediated by maternal mental health, they say, as “maternal preconception and pregnancy adiposity are known to increase the risk of various acute and chronic maternal mental health conditions”. The studies that adjusted for maternal mental health found weaker associations than those that did not.
There may also be mediation by gestational diabetes and hypertensive disorders of pregnancy, which frequently accompany maternal obesity and have been independently linked to child neuropsychiatric and behavioural disorders.
The authors could not rule out that confounders such as maternal and familial socio-economic positions, prenatal substance use, and parental mental health problems, which are linked with obesity, could contribute to the associations.
National Association of Specialist Obstetricians and Gynaecologists president Associate Professor Gino Pecoraro told TMR the review provided “further evidence of the association between increased maternal obesity and adverse pregnancy outcomes”.
“While it only shows an association rather than actual causation, there appears to be adequate evidence to encourage women to aim for a normal pre-pregnancy weight range to decrease the risks of adverse mental health outcomes in their children.”
He said previous studies had shown increased weight led to more gestational diabetes, pre-eclampsia and need for early and surgical delivery.
“It is time for more public education around the adverse effects of obesity on all aspects of reproduction and NASOG encourages government to help access to weight management programs for all pregnant and aspiring to be pregnant women,” Professor Pecoraro said.
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Asked how to broach the subject, given the double sensitivity of body weight and autism, he said he would mention weight gain during pregnancy at a first visit, say the average gain was up to 10-12kg, and outline the associations between excessive weight gain and adverse outcomes including behavioural or mental health issues in children.
“It is important to keep mothers on side and work with their doctors to manage weight gain rather than adopt a punitive or blaming stance, which does not help,” Professor Pecoraro said.
“We talk about diet and I frequently recommend a dietician review if I feel they can help. There are also usually inputs from dieticians in antenatal classes.
“I think the best approach would be to have awareness of ideal weight before women get pregnant to start off in a healthy weight range and be aware of what is an acceptable weight gain during pregnancy. Obesity can also have a deleterious effect on women wanting to get pregnant.
“I accept that both obesity and autism are ‘triggers’, but I think we need to get back to delivering factual scientific information to women so they can make their choices based on facts.
“There is too much emphasis at the moment on fads and social media-mediated misinformation … It seems every influencer and successful celebrity offers their view on pregnancy and childbirth and the opinion of trained obstetricians comes a distant second.
“I am reminded that we have become victims of our own success, where people forget that not all pregnancies result in ‘perfect’ outcomes, and sometimes we need to make sure that women have realistic expectations.”
