ADHD Linked to Post-Term Birth in New Study

Results of a new study conducted in The Netherlands found that children born post-term are at increased risk for behavioral and emotional problems, particularly attention-deficit hyperactivity disorder (ADHD).¹ Of 5145 infants born in The Netherlands, 382 (7%) were born post-term (at or after 42 weeks of gestation) and 226 (4%) were born pre-term (before 37 weeks of gestation). When the children were 18 months and 36 months, their parents completed a behavioral checklist, and the relationship between gestational age at birth and problem behavior was analyzed.

Compared with normal-term children, children born post term had a higher risk of overall behavioral problems and were more than twice as likely to have symptoms of ADHD. Factors such as mother’s weight and height, ethnicity, family income, alcohol consumption or smoking, education level, or the mother’s health during pregnancy were not associated with the findings.

The study authors offer several possible explanations for this association. One is that the placenta at the end of a late-term pregnancy is “old” and lacks the nutrients and oxygen that full-term fetuses require, predisposing them to abnormal development. Another explanation is that a disturbance in the “placental clock,” which controls the length of pregnancy, leads to hormonal abnormalities.

A limitation of this study is its reliance on subjective parental reporting instead of a clinical diagnosis from a clinician. Another limitation is that both gestational age and childhood behavior could have been influenced by other unknown social or medical factors. A strength of the study was that ultrasonographic dating was used to determine probable gestational age, which provides a more accurate estimate than if date of last menses was used.

Despite an association, no causality was proven. More research is needed to determine a causal relationship and whether the link between post-term birth and emotional and behavioral problems continues past age 36 months.

The causes of ADHD are unknown, although inherited genetic factors, environmental factors, and brain structure are thought to have some role.² Other risks of post-term birth include perinatal mortality, fetal dysmaturity syndrome, meconium aspiration syndrome, neonatal encephalopathy, and possibly cerebral palsy.^3,4

Pertinent Points:

- Post-term birth was associated with more behavioral and emotional problems in early childhood, especially ADHD.
- There is no evidence that being born at or after 42 weeks of gestation causes behavioral problems or ADHD.
 

References:

References
1. El Marroun H, Zeegers M, Steegers EA, et al. Post-term birth and the risk of behavioural and emotional problems in early childhood. Int J Epidemiol. 2012;[Epub ahead of print].
2. National Institute of Mental Health. Attention deficit hyperactivity disorder (ADHD): What causes ADHD? Accessed May 4, 2012.
3. Caughey AB, Butler JR. Postterm pregnancy. Updated March 25, 2011. Accessed May 4, 2012.
4. Moster D, Wilcox AJ, Vollset SE, et al. Cerebral palsy among term and postterm births. JAMA. 2010;304:976-982.