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A new study published in the Journal of Child Psychology and Psychiatry looked at maternal prenatal body mass index (BMI) and human fetal brain development.

“Given knowledge that the physical well-being of a mother during pregnancy is important for the long-term brain health of her child, we sought to discover whether and how maternal BMI may relate brain development in the womb,” study author Moriah E. Thomason told us. “It was already known that maternal prenatal BMI is related to cognitive and regulatory problems in childhood, but the neural correlates and their early developmental origins had yet to be addressed.”

BMI measures the body fat of adult women and men based on their weight and height. To calculate BMI, divide your weight in kilograms by the square of height in meters. The resulting number or BMI index, will put you in a category that’s either underweight, healthy weight, overweight, and obesity.

“We had a theory but also took a largely data-driven approach in order to be as impartial as possible,” Thomason told us. “We confirmed that brain areas linked to adult obesity are the areas where we observed significant effects of the fetus in utero.”

In the U.S. the amount of adults with a BMI index in the obesity category had been steadily rising since the last quarter century but has levelled off recently. However, older women aged 60 years and older continue to experience high BMI index rates.

“Prior studies provide evidence of cognitive delays in children born to high BMI mothers, but until now it has been difficult to attribute those differences to neural processes with prenatal onset,” Thomason told us. “For example, it is difficult to disentangle the influence of the postnatal environment on brain health and development in that child. We had been operating under the assumption that programming occurs during pregnancy to influence that child’s brain with lasting consequence, but we lacked evidence.”

According to the Centers for Disease Control and Prevention, National Vital Statistics Report, among women who gave birth in 2014, 3.8 per cent were underweight, 45.9 per cent were of normal weight, 25.6 per cent were overweight, 24.8 per cent were obese. Obesity during pregnancy has been known to increase the rate of C-section deliveries and babies that are born much larger than average, known as macrosomia.

“To test our theroy, we used resting-state MRI, a non-invasive technology, that utilizes information from spontaneous activity of the brain to construct circuits based on coordinated fluctuations in that data over time,” Thomason told us. “We sought to identify where the strength of connectivity (in the resulting circuits) showed differences related to maternal BMI.”

It is recommended by the Institute of Medicine that women follow weight gain guidelines during pregnancy, paying close attention to their BMI. While many women who are pregnant and obese were obese prior to their pregnancy, there is hardly any data that looks at BMI during pre-pregnancy.

“We discovered that connectivity in frontal and insula circuits varied with maternal BMI,” Thomason told us. “It is noteworthy that the significant fetal neural effects obtained in this study align so well with areas critical for integration of bodily information and areas previously implicated establishment of regulatory behaviors in children and adults.”

Thomason believes the implication of this work is that BMI of a mother relates to rapidly developing connections in her baby’s brain - even before that baby is born.

“This can be helpful in terms of recommendations made to expectant mothers and can be beneficial for understanding underlying mechanisms,” Thomason told us, “in this case specific neural connections, that may help to explain why children born to high BMI mothers sometimes show altered cognitive development.”