Pregnancy and ADHD: Overview
Pregnancy, while it cradles and nurtures the unborn infant, poses risks of its own to the child. Medical researchers know that harmful substances cross the placental barrier, but they do not know with any certainty if these substances lead to the development of ADHD in the child, although they suspect a link.
Maternal Use of Cigarettes and Alcohol
Pregnant mothers who continue smoking during their pregnancies, as well as mothers who drink alcohol while pregnant may potentially increase the chances of their children developing ADHD, according to the National Institutes of Mental Health.
Therefore medical professionals advise that as soon as a woman decides to become pregnant, or she suspects she is pregnant, she should stop drinking alcohol and smoking. In doing so, she is able to ensure that her unborn child has a better opportunity for good mental and physical health. 
Pregnancy and ADHD: Maternal Anxiety
Pregnant mothers worry about the health and well-being of their unborn children. Small, manageable amounts of stress during pregnancy are normal and to be expected; it’s the higher levels of stress that go on without being addressed that may affect the child after birth, reports WebMD.
Dr. Bea Van den Bergh of the Catholic University of Leuven in Belgium, along with several colleagues, studied 71 mothers and their first-born children from pregnancy through early childhood. The study was designed to measure maternal anxiety through the mothers’ pregnancies and assess the children for the development of ADHD and other behavioral disorders when the children were 8 and 9 years old.
The study showed a strong link between levels of maternal anxiety in early pregnancy and the susceptibility of the children to ADHD in childhood. This association was stronger than those seen for other potential predictors of ADHD –– smoking during pregnancy, the mother’s current stress level or low infant birth weight. These findings, called the “fetal programming hypothesis,” point up that environmental exposure to stress can significantly influence fetal brain development.
Van den Bergh, who authored the study, said, “This is some of the strongest evidence yet to suggest that anxiety during pregnancy influences the offspring’s risk for attention hyperactivity disorders.” 
Pediatric Brain Injury
Infants and children who have experienced brain injuries may develop symptoms that look like ADHD, reports the National Institutes of Mental Health. However, only a “small percentage” of children diagnosed with ADHD suffered any type of traumatic brain injury. 
There may also be some kind of genetic basis for ADHD - this is an active area of research interest and twin and adoption studies carried out by the National Institute of Mental Health (NIMH) have revealed that ADHD runs in families.
If researchers know which genes trigger the development of ADHD they may be able to devise ways of preventing it before a child starts showing signs of the disorder. Being able to target specific genes might also lead to more focused treatments. 
References and Photo Credit
 Salynn Boyles. Anxiety During Pregnancy Increases ADHD Risk. WebMD. 7/16/2004, retrieved at https://www.webmd.com/add-adhd/news/20040716/anxiety-during-pregnancy-increases-adhd-risk
 Attention Deficit Hyperactivity Disorder (ADHD). National Institute of Mental Health, retrieved at https://www.nimh.nih.gov/health/publications/attention-deficit-hyperactivity-disorder/complete-index.shtml
Image credit: Nutdanal Apikhomboonwaroot, https://www.freedigitalphotos.net/images/Family_g212-Infant_p29114.html