Focus on Preterm Birth and Psychiatric Disorders
Several recent articles have addressed the observation that psychiatric diseases occur more frequently in children and adults who were born preterm than at term. Psychiatric diseases that have an increased occurrence in children and adults who were preterm infants include schizophrenia, depression, autism and attention deficit hyperactivity disorder (ADHD). The research is focused on the reason for this increase; what is the mechanism behind the increase in psychiatric disorders and the preterm birth. There may be genetic factors, but most likely it is an interplay of environment and genes. It is interesting to speculate whether the exposures or genetic factors are prenatal, and thus may lead to both preterm birth and psychiatric disease, or if merely being a preterm infant in the NICU leads to psychiatric disease. This differentiation is important as the intervention to prevent the occurrence of psychiatric disease in preterm infants would differ depending on the mechanism.
While the role of the environment in preterm birth remains poorly investigated, one clear example of a prenatal exposure leading to both preterm birth and later psychiatric disease is maternal smoking during pregnancy. Women who are active smokers are more likely to deliver preterm than women who do not smoke. And infants born to women who smoke are more likely to have ADHD and other psychiatric disorders, than those babies unexposed in utero. Other examples of prenatal environmental exposures which lead to preterm birth and to psychiatric disorders include maternal stress and perinatal inflammation. Perinatal inflammation is associated with increased incidence of cerebral palsy in humans and animal models and there is a strong relationship with increased incidence of autism and schizophrenia in humans. It will be interesting to see if the Zika virus leads in some cases to psychiatric disorders and/or prematurity in offspring of women infected during their pregnancies. Although microcephaly has been the hallmark of Zika virus congenital infection, the critical windows of time of infection which may lead to different phenotypes such as prematurity or psychiatric disorders are not known.
Even without any prenatal exposures or genetic factors, being preterm and in a NICU may lead to exposures leading to psychiatric disorders later in life. Documented exposures include radiation, heavy metals, noise, sensory deprivation, ethanol, benzyl alcohol and other excipients, all known to be neurodevelopmental toxicants, and most leading to ADHD. While interventions exist, most NICUs have not yet incorporated them into their practice.
Defining the mechanisms, the genetics and the exposures is important in formulating interventions. Pregnant women are advised to avoid certain exposures that lead to preterm birth and may increase the likelihood of psychiatric disease later in life. NICUs must be mindful and reduce exposure to those developmental neurotoxicants known to cause developmental disturbances. The articles cited here address many of these issues, and pose many promising and as yet unanswered research questions.
