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Can pregnancy-related factors increase the risk of ADHD in children?

Attention-deficit and hyperactive disorder (ADHD) is a common mental disorder typically detected in childhood and is characterised by a short attention span, trouble controlling some behaviour (for example, waiting for one’s turn), or becoming overly physically active.

This topic particularly interests me. I am studying a BSc in Cognitive and Clinical Neuroscience and am currently doing a placement year at King’s College London; more importantly, I have a cousin who developed ADHD, which led me to do more research on this mental disorder. In this blog, I will be touching on some environmental factors which affect a child’s development, focusing on pregnancy.

It is important to note that I will be discussing research I have found which suggests that factors during this period may increase the risk of later development of ADHD, but there are many other risk factors of ADHD which all come into play and so the picture is far larger.

Also, the fact that studies show that some factors might be associated with ADHD — as in, they are both present in the same individual — does not prove that they are causally related — that these factors cause ADHD. But they might be important leads to understand this condition.

 

The early stages of an infant’s life are critical in the healthy development of the child and research has long shown that this strongly depends on the mother’s genes as well as her lifestyle, both during and after pregnancy.


Experiences or circumstances — the good, the bad, and everything in between — which are present in the early stages of life are critical to the healthy development of a child, both for their physical and mental well-being.


There are many factors that influence an infant’s cognitive development (how children think, explore and figure things out), and because of this, mothers are encouraged to be very careful, particularly during their pregnancy, as these lifestyle and environmental circumstances have the potential to have lifelong effects on their children.


The Role of Stress

Maternal stress during pregnancy can affect the development of the foetus which can result in a delay of cognitive and motor development (for example, a delay in jumping, walking and sprinting as well as a delay in acquiring knowledge and understanding through thoughts, experiences and senses) and possibly not being able to adapt well to stressful situations e.g. the child having constant fear and not being able to relax in a new environment.


However, the effects of maternal stress are not clearly shown in the early stages of the child’s development but rather later on. The negative outcomes in research have shown to be more clear cut at 8 months rather than 3 months.


Of course, the effects of prenatal (before birth) stress on infants' development seem rather mild, and these effects are only visible at a population level — by studying hundreds of women. Moreover, it’s difficult to establish during which period of pregnancy exposure to stress matters most to the development of the fetus.


Research suggests that stress during pregnancy, reflected by a high early pregnancy hassle or a strong fear of giving birth when the women are halfway into their pregnancy, is associated with lower mental and psychomotor developmental scores 8 months after the infant’s birth. This means that the higher the amount of daily hassle in early pregnancy and strong fears of giving birth, the lower mental development scores. The same pattern is found when fear of giving birth occurred late into pregnancy. This means that there could be the potential for a negative impact on the child’s ability of, for example, eye-hand coordination, or memory.


Recent findings show that mothers who experience high-stress levels or anxiety during pregnancy may be at a higher risk of having children with ADHD. This tells us that a mother experiencing stress is a very important factor and that this could be a factor influencing the possibility of their child developing ADHD.


But how can stress lead to the development of ADHD?

One possible explanation is the activity of the hypothalamic-pituitary-adrenal (HPA) axis. The HPA axis is our bodies’ in-built stress response centre and it includes the release of a stress hormone called cortisol, which helps us to cope when we are faced with a stressor, whether that be physical or psychological stress.


So, as we discussed in a previous blog, when experiencing high stress during pregnancy, we see increased levels of cortisol release.


The placenta acts as a major ‘barrier’ to cortisol and protects the baby from being exposed to too much cortisol as well as from the changes in stress hormones that occur around the time of labour. This increase in cortisol is required to boost the development of the unborn child, and in fact, an increase in this stress hormone improves the chances of the baby surviving in case of premature birth.


But, on the other hand, as you can imagine, too much of anything is not good for you, and prolonged exposure of stress throughout the pregnancy increases the levels of cortisol in the amniotic fluid (the fluid surrounding the baby in the mum’s tummy).


The role of diet, obesity and use of substances


Another risk factor for children’s cognitive development is maternal obesity, and this is considered to be one of the most pressing health problems in this day and age.

A pregnant mother having a poor diet — i.e., not obtaining the required nutrition for a healthy outcome — could be harmful to the developing baby as they would not be getting enough nutrition that is required for growth, which may lead to “low birth weight”, that is, babies that are smaller at birth.

Research suggests that people who are born with low birth weight are at a higher risk of developing ADHD. Therefore, as always recommended, it is important for mothers to ensure they are consuming all the required nutrition during pregnancy.

You may have heard of something called BMI, which is ‘body mass index’. This is a person’s weight in kilograms divided by the square of height in meters. It is an inexpensive and easy screening method for categorising weight — underweight, healthy weight, and overweight.

Maternal BMI, so a mothers BMI during pregnancy, has been positively associated with difficulties in regulating emotions and high inattention scores in five-year-old children, as reported by their teachers. Studies show lower cognitive performance is also observed in children whose mothers have maternal weight gain during pregnancy.

However, a population-based study found that although high pre-pregnancy BMI increases the risk of ADHD in children, the association is lost when the baby's sibling's BMI is taken into consideration in the analyses, which suggests that further unidentified risk factors may contribute to the propensity to both increased BMI and increased ADHD risk.

Interestingly, racial and ethnic background may also play a role in the effects of maternal BMI on the susceptibility of the infant for later development, as suggested by a study which reported that maternal obesity is associated with an increased risk of ADHD in children born to Caucasian women, but not to African American women.

There is also an interesting pattern of association between ADHD and substance abuse disorder. Use of drugs during pregnancy can have a direct effect on the fetus, whether it is smoking, drinking alcohol, or even consuming larger amounts of caffeine than recommended. Relevant to ADHD, these substances can affect the child’s developing brain, potentially leading to memory and attentiveness problems.

 

There are many external factors that contribute to an infant’s development and the role of the mother before, during, and after pregnancy that cannot be underestimated.

Factors such as stress, obesity, and drug abuse are seen to be associated with ADHD, and controlling these risk factors as best as possible during pregnancy may be important to prevent the risk of developing ADHD.

However, we cannot make the assumption that all of these factors directly cause ADHD due to the many factors reported to contribute to ADHD.

Later development of ADHD is not all down to a mother’s actions during pregnancy or even genes, but the genes and environment balanced to contribute to the development of every individual.

 


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