New research has found that babies who are post-term — defined as born after a normal-length pregnancy of 42 weeks — are more likely to have behavioral and emotional problems in early childhood, including attention deficit/hyperactivity disorder (ADHD).
“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,” said Hanan El Marroun, Ph.D., lead author of the study.
The study found a U-shaped association between gestational age at birth and behavioral and emotional problems in early childhood. This indicates that both preterm and post-term children are at higher risk for problems, the researcher says.
The study was embedded in the Generation R Study, a large population-based study based in Rotterdam. Pregnant mothers who were due to give birth between April 2002 and January 2006 were asked to participate by their midwives and gynecologists.
The researchers measured gestational age using ultrasound, a method thought to be superior to date of last period. Based on this measure, out of 5,145 babies, 382 (7 percent) were born post-term and 226 (4 percent) were born pre-term.
A standardized and validated behavioral checklist (Child Behavior Checklist, CBCL/1.5-5) was used to assess the children. At 18 and 36 months old, a questionnaire was sent to the mother and the father was also sent a questionnaire when the child was 36 months.
Several potential explanations were offered by the researchers for the increased problems, including a higher risk of perinatal problems known to be associated with larger babies.
Also considered was uteroplacental insufficiency, a situation in which an “old” placenta offers fewer nutrients and less oxygen than required by a full term fetus. This lack of nutrients and oxygen may lead to abnormal fetal development which, in turn, may lead to abnormal emotional and behavioral development, the researchers said.
Another explanation offered by the researchers was the potential disturbance of the “placental clock,” which controls the length of pregnancy and regulates the maternal and fetal hypothalamic-pituitary-adrenal axis (HPA-axis).
It has been suggested that placental endocrine malfunctioning or maternal stress at critical times during fetal development may influence the fetal HPA-axis, leading to neuroendocrine abnormalities that could increase the child’s vulnerability to emotional and behavioral problems later in life.
The researchers caution that longer followup is necessary to establish whether the relationship between post-term birth and behavioral problems persist beyond 36 months.
The research was published in the International Journal of Epidemiology.
Source: Oxford University Press