Babies who are born too soon or arrive weighing too little are about three times more likely to develop attention deficit hyperactivity disorder (ADHD) than full-term, healthy-sized infants, a research review suggests.
Researchers examined data from 12 previous studies with a total of 1,787 participants and found that even among these high-risk babies, the odds of ADHD increased as babies spent fewer months in the womb and were born at even tinier sizes.
“There is robust evidence that very preterm or very low birth weight individuals have an increased risk of ADHD,” said senior study author Dr. Carlos Renato Moreira-Maia of the Federal University of Rio Grande do Sul in Porto Alegre, Brazil.
It’s possible that the stress of the early birth or premature development of vital organs and systems in the body might lead to inflammation and hormonal changes that contribute to ADHD, Moreira-Maia said by email.
Many factors including mothers’ medical histories as well as smoking, eating and drinking habits during pregnancy can influence the odds of preterm birth or an underweight infant, and these things might also contribute to ADHD in kids, Moreira-Maia added.
“The reasons for increased vulnerability to ADHD in preterm/low birth weight individuals remain unknown,” Moreira-Maia said.
Pregnancy normally lasts about 40 weeks, and babies born after 37 weeks are considered full term. The study focused on the most vulnerable preterm infants, delivered before 32 weeks’ gestation or weighing less than 1,500 grams (3.3 pounds) at birth.
In the weeks immediately after birth, preemies often have difficulty breathing and digesting food. They can also encounter longer-term challenges such as impaired vision, hearing and cognitive skills, as well as social and behavioral problems.
For the current study, researchers looked at data on healthy babies who were born weighing at least 2,500 grams (5.5 pounds) or arrived after 37 weeks’ gestation and they also considered smaller, earlier arrivals.
Compared with these healthy babies, infants born at less than 32 weeks’ gestation or weighing less than 1,500 grams (3.3 pounds) were more than twice as likely to develop ADHD, researchers report in Pediatrics.
When babies were born at less than 28 weeks’ gestation or weighing less than 1,000 grams (2.2 pounds) their odds of ADHD were more than four times higher than healthy infants, the study also found.
One limitation of these results is that all but one of the smaller studies in the analysis was done in a high-income country, which means the results may not reflect what might happen in lower-income nations, the authors note.
Even so, the findings offer fresh evidence of the connection between an ADHD diagnosis and starting life too early or weighing too little, said Joel Nigg, author of an accompanying commentary and director of the ADHD and Attention Disorders Program at Oregon Health and Science University in Portland.
Women, in high-income countries where malnutrition isn’t a concern can help to minimize their odds of having a preterm or underweight baby by doing several things during pregnancy, Nigg advised. These include eating well, gaining a healthy amount of weight, not smoking, avoiding stress and getting enough sleep.
When they do have preemies or underweight babies, women may still be able to minimize the chances of ADHD by breastfeeding infants as long as possible and making sure babies get plenty of calories, Nigg said.
“If you have a low birth weight or pre-term baby, follow medical advice,” Nigg said by email. “But the first principle is nutrition, nutrition, nutrition.”