Lead author Hanan El Marroun, explained:
"Post-term children have a considerably higher risk of clinically relevant problem behavior and are more than twice as likely as term born children to have clinical ADHD.
Further research is needed in order to determine the causes of post-term birth and to minimize the long-term consequences. It is also important that further research is carried out in order to demonstrate a causal relation between post-term birth and behavioral problems and longer follow ups would also be advantageous."
The study which looked at 5,145 babies from the Netherlands found a U-shaped association between behavioral and emotional problems in early childhood and gestational age at birth. According to the researchers, this finding suggests that children born both preterm and post-term are more likely to develop problems.
Children born after 42 weeks of pregnancy were nearly 50% more likely to suffer behavioral and emotional problems and were more likely to have ADHD.
The study was embedded in the Generation R Study, a large population-based prospective cohort study from fetal life onwards.
The researchers enrolled expectant mothers in Rotterdam who were due to give birth between April 2002 and January 2006 to participate in the study.
The team measured gestational age using ultrasound and found that out of the 5,145 babies, 4% (226) were born pre-term and 7% (382) were born after 42 weeks.
The researchers, who used a standardized and validated behavioral checklist (Child Behavior Checklist, CBCL/1.5-5) in order to evaluate the children, sent a postal questionnaire to the mothers at 18 and 36 months. In addition, the father also received a questionnaire when the child was 36 months of age.
Results showed that at 18 and 36 months, both post-term and pre-term babies were at higher risk of behavioral and emotional problems.
An additional analysis has observed comparable results when children, whose gestational age was measured in the second or third trimester, were excluded and the results failed to appear and be explained by various factors, such as the mother's weight and height, family income, ethnicity, alcohol and cigarette consumption, the level of education or maternal psychopathology in mid-term.
They highlight, however, that even though the study controlled for a large number of covariates, other factors, such as maternal malnutrition during pregnancy, cannot be excluded.
According to the researchers, there are several potential explanations for their findings, such as the increased risk of perinatal problems known to be associated with larger babies.
However, their findings did not change when the team excluded babies that weighed over 4,000 grams at birth and those that were induced.
Another possible explanation may be uteroplacental insufficiency; the situation in which an "old" placenta provides less oxygen and nutrients than a full term fetus requires.
Insufficient oxygen and nutrients may trigger abnormal fetal development, which may result in abnormal behavioral and emotional development. However, as the study was observational they researchers were unable to distinguish possible effects of uteroplacental insufficiency from perinatal problems.
Furthermore, the team highlight the potential disturbance of the "placental clock" which controls the length of pregnancy and regulated the maternal and fetal hypothalamic-pituitary-adrenal axis (HPA-axis).
According to the research, the fetal HPA-axis may be influenced by placental endocrine malfunctioning or maternal stress at critical times during fetal development. They explain that this influence may result in neuroendocrine abnormalities that could increase how susceptible a child is in the future to emotional and behavioral problems.
And lastly, they explain that the same cause may underlie being born after 42 weeks and having behavioral problems. For instance, neurodevelopmental factors associated to behavioral problems could be involved in the complex process of birth.
According to the researchers, longer follow-up is required in order to determine if the association between post-term birth and behavioral problems continues after 36 months. In addition, they also suggest that practitioners involved in management of prolonged pregnancy should take note of their findings.
Written By Grace Rattue