The role of fetal inflammatory response syndrome and fetal anemia in nonpreventable term neonatal encephalopathy

Neuroimaging findings associated with the fetal inflammatory response syndrome

The fetal inflammatory response syndrome (FIRS) is a condition whereby the fetus mounts an inflammatory response to intrauterine infection/inflammation. Clinical consequences include preterm premature rupture of membranes (PPROM), spontaneous preterm delivery, neonatal sepsis, bronchopulmonary dysplasia, and brain and other organ injury. Mechanisms leading to brain injury in FIRS have been investigated in animal and human studies. We review the neuroimaging findings of brain injury in FIRS, which overlap those of hypoxic-ischemic injury, and clinical correlation is necessary for a correct diagnosis. FIRS should be considered the primary diagnosis when neuroimaging findings such as periventricular leukomalacia are identified in preterm children born as a consequence of PPROM and spontaneous preterm labor. Additionally, FIRS should be considered in term infants who do not have the most common features of HIE (e.g. a sentinel event). Systematic histopathologic examination of the placenta and umbilical cord and/or detection of characteristic inflammatory markers in such cases are needed to establish the correct diagnosis.

Mechanisms of brain injury in newborn infants associated with the fetal inflammatory response syndrome

The fetal inflammatory response syndrome (FIRS) is characterized by umbilical cord inflammation and elevated fetal pro-inflammatory cytokines. Surviving neonates, especially very preterm infants, have increased rates of neonatal morbidity including neurodevelopmental impairment. The mechanism of brain injury in FIRS is complex and may involve "multiple hits." Exposure to in utero inflammation initiates a cascade of the fetal immune response, where pro-inflammatory cytokines can cause direct injury to oligodendrocytes and neurons. Activation of microglia results in further injury to vulnerable pre-myelinating oligodendrocytes and influences the integrity of the fetal and newborn's blood-brain barrier, resulting in further exposure of the brain to developmental insults. Newborns exposed to FIRS are frequently exposed to additional perinatal and postnatal insults that can result in further brain injury. Future directions should include evaluations for new therapeutic interventions aimed at reducing brain injury by dampening FIRS, inhibition of microglial activation, and regeneration of immature oligodendrocytes.

FIRS: Neonatal considerations

Fetal Inflammatory Response Syndrome (FIRS) is the fetal counterpart of systemic inflammatory response syndrome (SIRS) described in adults. When the fetus is directly exposed to inflammation of the fetal membranes or the placental-fetal circulation, and organs are adversely affected, the disorder is known as FIRS. This syndrome can significantly affect multiple organs with significant short and long term implications for the newborn. In cases of neonatal encephalopathy when no obvious etiology is identified, FIRS needs to be considered. Based on the significant incidence of chorioamnionitis and its potential effects on the newborn, any evidence of maternal, fetal, or neonatal infection should mandate further evaluation of the placenta and membrane histopathology.

Evaluation for the etiology of neonatal encephalopathy and the diagnosis of FIRS

A common disorder managed in the neonatal intensive care unit (NICU) is neonatal encephalopathy (NE). There are multiple causes of NE, including hypoxic-ischemic encephalopathy (HIE) and the fetal inflammatory response syndrome (FIRS). It is important to ascertain the specific cause of NE in an affected child, as it may affect the clinical management and will assist in prognostication. This paper discusses the background of inflammatory damage to the fetal brain, the history of FIRS as a clinical diagnosis, the characteristics of infants with FIRS, and methods to evaluate the etiology of NE.

Early development of the human placenta and pregnancy complications

An adequately sized placenta at a suitable site with appropriate depth and centripetal progression of implantation are the major factors for optimal fetal development. The cytotrophoblasts surround the blastocyst fuses at the site of the uterine attachment. This forms a second layer of multinucleated syncytiotrophoblasts that constitutes the inner epithelial boundary of the chorionic villous against the intervillous space. In a normal pregnancy, extravillous cytotrophoblasts (EVT) invade and obstruct the spiral arteries and remodel them. Vacuoles in the syncytial cell layer fuse and develop the intervillous space. The inner cell mass (embryoblast) gives rise to the umbilical cord and the mesenchyme in the chorionic villi. Vasculogenesis starts with the formation of hemangioblastic cords in this mesenchyme. The trophoblastic cell columns anchor the placenta. A variety of molecular pathways participate in the placentation process. Placental morphogenesis occurs mainly through complex cellular interactions between the chorionic villous and the extravillous cytotrophoblasts. The formation of the normal structure of the chorionic villi, syncytiotrophoblast layer and vasculature is essential for placental function, hormone production, and regulation of fetal growth. At each stage of placental development, genetic variants, exposure to infection, poor vascular function, oxidative stress, or failure of normal development can all lead to abnormal formation resulting in the clinical complications of pregnancy such as fetal growth disorders, neonatal neurologic abnormalities, placental adhesions, and inflammatory problems as well as maternal disease such as preeclampsia.

Perinatal Anemia is Associated with Neonatal and Neurodevelopmental Outcomes in Infants with Moderate to Severe Perinatal Asphyxia

BACKGROUND

Perinatal anemia may cause perinatal asphyxia. Its pathophysiology and neurodevelopmental effects are theoretically different from other causes of perinatal asphyxia.

OBJECTIVE

The study aimed to determine whether perinatal anemia results in different short-term and long-term outcomes than other causes of perinatal asphyxia treated with therapeutic hypothermia.

METHODS

We retrospectively included infants with moderate to severe hypoxic-ischemic encephalopathy, born between May 2009 and October 2015. During follow-up, we assessed cognitive and motor development at 2-3 years of age, using the Bayley Scales of Infant and Toddler Development, third edition (BSID-III). Neurodevelopmental outcome (NDO) was classified as abnormal in case of cerebral palsy with Gross Motor Function Classification System ≥III and/or a BSID-III composite score < 85. Outcomes of infants with perinatal anemia (initial hemoglobin < 7 mmol/L) were compared to infants born with perinatal asphyxia due to other causes.

RESULTS

In total, 111 infants were included of whom 30 infants (27%) died during the neonatal period. Infants with anemia (n = 23) had a higher mortality risk, OR 3.33, 95% CI 1.27-8.72, p = 0.01. None of the surviving infants with anemia (n = 12) had an abnormal NDO, in contrast to 26/69 (38%) with neurodevelopmental impairments, particularly motor problems, in the non-anemic group, p < 0.01.

CONCLUSIONS

Perinatal anemia causing moderate to severe perinatal asphyxia is associated with a higher risk for neonatal mortality. All survivors with perinatal anemia, however, showed a normal NDO in contrast to children who were born asphyxiated due to other causes. The underlying pathophysiological mechanism for the favorable NDO in the perinatal anemia group needs further elucidation.