Perinatal Neuroprotection in Preterm Birth

Abstract

Preterm birth is one of the main causes of perinatal morbidity and mortality. The rate of grade III and IV cerebral hemorrhages in infants with a birth weight of less than 1500 g in Germany in 2022 was 2.97% and the periventricular leukomalacia rate was 1.07%. In addition to these severe forms of brain damage which are visible on sonography, recent MRI studies carried out at the calculated due date of affected children also showed diffuse white and grey matter injuries, especially of the basal ganglia and the cerebellum, indicating impaired brain development and function. To offer these children the best possible start in life it is essential that they are cared for in a level I perinatal center right from the start. In addition, a number of perinatal measures are available which may significantly improve the neuronal development in preterm infants. They include the use of antenatal corticosteroids and magnesium as well as deferred cutting of the umbilical cord. Recent studies have shown that in contrast to term-born infants, hypothermia treatment is unsuitable for neuroprotection in premature babies. As secondary and tertiary cell damage may occur days or even weeks after the primary insult due to persistent inflammation and the lack of trophic stimulation, in addition to providing premature infants with the best possible initial care, it is also necessary to optimize subsequent care in the intensive care unit in terms of providing a neuronal-positive stimulating environment. Breastfeeding and supply of breast milk are particularly important in this context.

Keywords

preterm birth - periventricular-intraventricular hemorrhage - neuroprotection - periventricular leukomalacia

Introduction

Preterm birth is one of the most important causes of perinatal morbidity and mortality, with around half of all cases of perinatal mortality occurring in preterm babies weighing less than 1500 g [1]. Although the incidence of preterm birth in Germany has continually decreased from 8.87% in 2014 to 7.87% in 2023, the mortality of extremely preterm infants remains high [2]. Many of the children who survive are severely affected by brain damage, much of which occurs postnatally. In individual cases, however, there are indications that brain damage had an antenatal genesis. Brain damage usually has multifactorial origins. Causes include hypoxia/ischemia and ascending infection as well as cardiovascular changes resulting from invasive ventilation or other invasive interventions required due to the immaturity of the infant ([Fig. 1]) [3] [4] [5] [6] [7]. The rate of grade III and IV cerebral hemorrhages in babies with a birth weight of less than 1500 g in 2022 was 2.97% and the rate of periventricular leukomalacia was 1.07% [2].

Fig. 1 Perinatal brain damage in preterm infants is caused by a number of factors. They include hypoxia/ischemia, ascending infection as well as cardiovascular changes resulting from invasive ventilation or other invasive interventions required because of the immaturity of the infant. This leads to cell loss from astrogliosis, changes in oligodendrocyte development and consequently impaired myelination. Interventions to reduce brain damage in affected infants are possible in every phase, i.e., the primary, secondary, or tertiary phase, after the original insult [8]. Source: Molloy EJ, El-Dib M, Soul J et al. Neuroprotective therapies in the NICU in preterm infants: present and future (Neonatal Neurocritical Care Series). Pediatr Res 2024; 95: 1224–1236. DOI: 10.1038/s41390-023-02895-6. © The Author(s) 2023. Licensed under a Creative Commons Attribution 4.0 International License (https://creativecommons.org/licenses/by/4.0/). Adapted.).

In addition to these severe, sonographically visible forms of brain damage, MRI of affected children carried out on the calculated due date also shows diffuse white and gray matter injuries, especially of the basal ganglia and the cerebellum which are indications for impaired brain development and function [9]. Morphologically this is caused by astrogliosis and insufficient maturation of oligodendrocytes, which leads to impaired myelination due to persistent inflammation and a lack of growth factors [10] [11] [12] [13] [14]. Experimental studies show that this inflammation and inadequate trophic stimulation result in further cell damage occurring in the days and weeks subsequent to the primary insult. This is known as the primary, secondary, and tertiary phase of the insult [8].

Although the prevalence of infantile cerebral palsy as a late sequelae of severe neuronal damage is currently 6.5–12% and has declined following improvements in clinical care in recent years, the rate of additional neurological disorders such as cognitive impairment, impaired vision, hearing impairment, behavioral disorders, and psychiatric disorders in extremely preterm infants is estimated to be 25–50% [15] [16] [17] [18].

A number of perinatal measures are now available which can significantly improve the neuronal outcomes of preterm infants. This review throws a light on currently available neuroprotective strategies which are primarily aimed at countering the primary insult. Neonatology interventions which can improve the neuronal outcome days and even weeks after birth are also discussed.

Search of the Literature

A selective search of the literature up until December 2024 was carried out in PubMed using the key terms “neuroprotection,” “intra-/periventricular hemorrhage,” “periventricular leucomalacia,” “preterm birth,” “preterm delivery.” The starting point was our last review on this issue [19]. Relevant prospectively randomized studies, meta-analyses and review articles were selected for this article. Cross-references to other important works were considered.

Neuroprotective Strategies in the Primary Phase

Morphology of the germinal matrix

The overwhelming majority of neonatal cerebral hemorrhages start in the germinal matrix [20]. If we want to understand the approach used for neuroprotective strategies against this form of injury, it is first necessary to engage with the specific morphology of this region of the brain.

In contrast to other brain areas such as the cerebral cortex or white brain matter, the germinal matrix is characterized by very strong angiogenesis. The extremely rapid endothelial proliferation results in a high vascular density. The pronounced vascularization of the germinal matrix is the result of the high energy needs of neuronal and glial precursor cells which migrate from here into the different brain regions where they mature further [21].

Rapid angiogenesis in the germinal matrix is accompanied by inadequate maturation of the blood vessels. Pericytes are an essential component of the walls of capillaries, venules, and arterioles ([Fig. 2]) [22]. They are embedded in the basement membrane and cover the endothelial cells. Pericytes play a decisive role in directing angiogenesis. They stabilize vascular structures, maintain the blood-brain barrier and control the neurovascular unit, i.e., the endothelium, astrocytes and neurons [23] [24] [25] [26]. If they are stimulated by angiogenetic factors such as platelet-derived growth factor-B (PDGF-B), angiopoietin, sphingosine-1-phosphate or transforming growth factor β (TGFβ), they degrade the basement membrane, induce the formation of new blood vessels, stabilize the structure of new blood vessels by synthesizing extracellular matrix components, and promote maturation of the corresponding endothelial cells [27] [28].

Fig. 2 Cross-sectional diagram of the blood-brain barrier: endothelium with tight junctions, basement membrane, pericytes, astrocyte end-feet [21]. GFAP = glial fibrillary acidic protein. Reprinted from Clinics in Perinatology, Volume 41, Issue 1, Praveen Ballabh, Pathogenesis and Prevention of Intraventricular Hemorrhage, 47–67, 2014, with permission from Elsevier. The Creative Commons license does not apply to this content. Any further use is subject to permission from Elsevier. [rerif]

Compared to other areas of the brain, the vascular walls in the germinal matrix have few pericytes [29]. This is probably a consequence of the low TGFβ concentrations in the uterus and in the initial days after birth. The low TGFβ level stimulates endothelial proliferation, leading to strong angiogenesis which is characterized by unstable vascular walls due to the lack of pericytes [21].

The basement membrane is another important component contributing to vascular stability ([Fig. 2]). It consists of laminin, collagen, fibronectin, and the heparan-sulfate proteoglycan perlecan [30] [31] [32]. Postmortem examinations of extremely preterm neonates have shown that fibronectin concentrations in the blood vessels of the germinal matrix are significantly lower than in other brain regions ([Fig. 2]) [33]. Similar to pericytes, synthesis of the basement membrane is stimulated by TGFβ. Low TGFβ levels are associated with an immature basement membrane and, consequently, with unstable vascular walls [21].

The endothelium, basement membrane and pericytes are encased by astrocyte end-feet ([Fig. 2]). Astrocyte end-feet are an essential component of the blood-brain barrier; they consist of intermediate filaments whose major component is glial fibrillary acidic protein (GFAP) [34]. Postmortem studies of preterm babies have shown that the GFAP content of astrocytes in the germinal matrix is lower than in other brain regions and end-feet coverage of the vascular walls is similarly lower ([Fig. 3]) [35]. This finding is another contributary cause to the instability of the vascular network in the germinal matrix [36] [37] [38].

Fig. 3 Compared to white matter vasculature, germinal matrix vessels are characterized by fibronectin deficiency and lower astrocyte end-feet coverage [21]. a Representative frozen section through the germinal matrix and white matter in a preterm infant aged 24 GW. Fibronectin, visualized here in red with immunofluorescence, is strongly expressed in the white matter vasculature but not in germinal matrix vessels (arrows). Scale: 20 µm. b Representative frozen section through the germinal matrix and white matter in a preterm infant aged 24 GW. The endothelium is visualized in red with immunofluorescence and glial fibrillary acidic protein (GFAP) in the astrocytes is green. GFAP-positive astrocyte end-feet are wrapped closely around the external endothelium in white matter vasculature but are barely present in the germinal matrix (arrows). Scale: 20 µm. Reprinted from Clinics in Perinatology, Volume 41, Issue 1, Praveen Ballabh, Pathogenesis and Prevention of Intraventricular Hemorrhage, 47–67, 2014, with permission from Elsevier. The Creative Commons license does not apply to this content. Any further use is subject to permission from Elsevier. [rerif]

Measurement of hypoxia-inducible factor-1α indicates that oxygen concentrations in the germinal matrix are lower than in the adjacent white brain matter. This is probably due to the high oxygen requirements of the neuronal and glial precursor cells found in white matter. A low oxygen concentration activates the release of vascular endothelial growth factor (VEGF) and angiopoietin and simultaneously inhibits TGFβ. This stimulates angiogenesis. Immature vessels are formed, which consist almost exclusively of endothelial cells with a low percentage of pericytes, decreased fibronectin in the basement membrane, and reduced GFAP concentrations in the astrocytes [21].

It is interesting in this context that intraventricular hemorrhages occur predominantly in the first three days of life and that the incidence of intraventricular hemorrhage decreases strongly thereafter [20]. This is very probably due to increasing oxygenation of the germinal matrix, which results in a decrease in VEGF and angiopoietin and an increase of TGFβ which inhibits angiogenesis [21].

Antenatal steroids (ANS)

It is well-known and confirmed in a recent meta-analysis that ANS administration reduces neonatal mortality (RR 0.78, 95% CI 0.70–0.87), respiratory distress syndrome (RDS) (RR 0.71, 95% CI 0.65–0.78) and the rate of intraventricular hemorrhage (RR 0.58, 95% CI 0.45–0.75) [39].

For many years it was assumed that glucocorticoids only improve neonatal outcomes by reducing the incidence of RDS. A stable respiratory situation reduces the need for numerous interventions in neonates such as suctioning and the placement and replacement of access lines, etc., which can trigger strong fluctuations in cerebral blood flow. As very immature preterm infants have limited cerebral autoregulation [40], this leads to strong pressure fluctuations in the very vulnerable vasculature of the germinal matrix. The consequence is intraventricular and periventricular hemorrhage [20] [41].

Experimental studies in animals and postmortem studies in human fetuses have shown that antenatal administration of betamethasone suppresses endothelial proliferation ([Fig. 4]). Betamethasone administration contributes to stabilizing the vasculature by enhancing pericyte coverage and elevating GFAP concentrations in astrocytes. These changes are driven by glucocorticoid-induced inhibition of VEGF and increased release of TGFβ [29] [33] [42].

Fig. 4 Glucocorticoids suppress endothelial proliferation [42]. a Pregnant rabbits were administered 0.2 mg/kg betamethasone on days 27 and 28 of gestation. Rabbit fetuses were delivered by caesarean section on day 29 of gestation (due date: 32nd day of gestation) and their brains were examined. The upper two images show representative frozen sections of the germinal matrix. The endothelium was visualized immunohistochemically with CD 31 antibodies (red), Ki67 (green) was used as the proliferation marker. Double staining (endothelial proliferation; arrows) was not observed after betamethasone administration. Scale 20 µm. b Representative cross-section through the germinal matrix and white brain matter of two infants aged 23 GW with and without the administration of betamethasone. The endothelium was visualized immunohistochemically with CD 34 antibodies (red); Ki67 (green) was used as the proliferation marker. Double staining (endothelial proliferation; arrows) was seen much less after betamethasone administration. Scale: 50 µm. Source: Govindaiah Vinukonda, Krishna Dummula, Sabrina Malik, Furong Hu, Carl I. Thompson, Anna Csiszar, Zoltan Ungvari, and Praveen Ballabh, Effect of Prenatal Glucocorticoids on Cerebral Vasculature of the Developing Brain, Stroke, 2010, Volume 41, Number 8, 1766–1773, DOI: 10.1161/strokeaha.110.588400, The American Heart Association, with permission from Wolters Kluwer Health Inc. The Creative Commons license does not apply to this content. Use of this material in any format is prohibited without written permission from the publisher, Wolters Kluwer Health, Inc. Please contact [e-mail] for further information. [rerif]

Unfortunately, there are no experiments showing how long the effects of betamethasone on the vascular morphology persist. However, a recent observational study by Clyman et al. has investigated whether the rate of intraventricular and periventricular hemorrhage in extremely preterm infants < 28 GW (N = 410) rises again if the infants are born more than 10 days after the antenatal administration of betamethasone [43]. The study also investigated whether a second administration of ANS 10 days after the first administration could prevent a possible increase in cerebral hemorrhages. Multivariable regression showed that the severe cerebral hemorrhage rate in infants born 10 days after ANS administration was significantly higher compared to infants born between one and nine days after ANS administration (OR [95% CI]: 2.9 [1.1–7.2]). Of the 120 infants born 10 days or more after the first administration of ANS, 64 (53%) received a second cycle of betamethasone. The rate of severe cerebral hemorrhages in these children was not higher than that of the group of infants born between one and nine days after the first ANS administration and was significantly lower than that of infants born 10 days or more after the first ANS administration who did not receive a second dose (OR [95% CI]: 0.1 [0.02–0.65]) [43]. This would indicate that the effect of glucocorticoids on vascular stability in the germinal matrix is merely transient.

The benefits of ANS administration on the rate of cerebral hemorrhage are especially obvious in fetuses aged ≤ 30 GW; the effect disappears in older fetuses [44]. This is due to the increasing regression of the germinal matrix with advancing gestational age. From week 36 of gestation, the germinal matrix is barely detectable [21].

In other words: based on the currently available data, omitting to administer ANS after 30 weeks of gestation is not associated with an increased risk of cerebral hemorrhage. However, the possibility cannot be excluded that ANS administration may have a neuroprotective effect on smaller, sonographically invisible lesions in fetuses aged more than 30 GW. On the other hand, adverse effects on the further development of children have been reported for ANS administration and delivery after 37 weeks of gestation [45] [46]. The administration or omission of ANS therefore remains a difficult decision and the risks and benefits must be weighed up.

Magnesium

Antenatal intravenous high-dose administration of magnesium sulfate already demonstrated a neuroprotective effect in premature babies with a birth weight of < 1500 g in observational studies carried out in the 1990s [47]. Those observations have since been verified in numerous prospective randomized studies. The most recent meta-analysis published in 2024 included six studies with 5917 patients and 6759 babies born < 34 GW in its randomization [48]. All the studies were carried out in high-income countries (2 in the USA, 2 across Australia and New Zealand, 1 each in Denmark and France) between 1995 and 2018. The primary study outcomes “cerebral palsy” (RR 0.71, 95% CI 0.57–0.89) and “death or cerebral palsy” (RR 0.87, 95% CI 0.77–0.98) at two years of corrected age were reduced significantly by the antenatal administration of magnesium sulfate. Magnesium did not have a significant effect on mortality at the age of two years nor on further development at school age ([Table 1]) [48].

Table 1 Perinatal neuroprotection for preterm infants born < 34 + 0 GW after antenatal magnesium.

	RR (95% CI)	Number of children (Number of RCT)	Level of evidence (GRADE)
Meta-analysis of the neuroprotective effect of antenatal magnesium in premature children born < 34 + 0 GW [48]. 95% CI = 95% confidence interval; GRADE = Grading of Recommendations Assessment, Development and Evaluation; RCT = randomized controlled trial; RR = relative risk
Cerebral palsy at the age of 2 years	0.71 (0.57–0.89)	6107 (N = 6)	High
Mortality or cerebral palsy at the age of 2 years	0.87 (0.77–0.98)	6481 (N = 6)	High
Mortality at the age of 2 years	0.96 (0.82–1.13)	6759 (N = 6)	Moderate
Severe neuronal development disorders at school age	0.92 (0.53–1.62)	940 (N = 2)	Very low

Numerous mechanisms which can mediate the neuroprotective effect of magnesium have been investigated in experiments. Large amounts of excitatory amino acids such as glutamate, succinate, etc. are released presynaptically during acute cerebral ischemia. These neurotransmitters activate neuronal N-methyl-D-aspartate (NMDA) receptors which regulate calcium channels. As a result, large amounts of calcium ions flow down an extreme extra-intracellular concentration gradient into the cell. An excessive increase of intracellular calcium levels leads to cell damage through the activation of proteases, lipases, and endonucleases [49]. Magnesium ions regulate the voltage-dependent NMDA channels and protect the brain from lesions mediated by the NMDA receptors [50] [51]. Magnesium additionally suppresses cerebral seizures and is an effective vasodilator [52] [53]. Both effects are neuroprotective. Magnesium also decreases the release of nitrogen oxide and thereby reduces the post-ischemic production of oxygen radicals [54].

Experimental studies have shown that antenatal administration of magnesium induces protective preconditioning in the immature brain [55]. When magnesium was administered between twelve hours and six days before a hypoxic-ischemic insult, subsequent brain damage was markedly lower. Magnesium modulates the synthesis of mRNAs/miRNAs which are involved in mitochondrial functioning and metabolism. Analysis of the metabolome (H+-NMR) showed that magnesium attenuates the hypoxic-ischemic induced increase in succinate in the brain and reduces depletion of high-energy phosphates. Succinate is an excitatory neurotransmitter which causes neuronal cell damage if it is present in high concentrations. The administration of magnesium also preserves mitochondrial respiration, reduces oxygen free radical formation, and remediates inflammatory processes after a hypoxic-ischemic insult [55].

Management of cord clamping

The transition of the fetal circulation from the intrauterine to the postnatal status is an extremely vulnerable phase for the immature brain. As mentioned above, extremely preterm neonates have very limited cerebral autoregulation [40]. Strong fluctuations in systemic blood pressure therefore pass unhindered into the cerebral vascular bed, where they cause intraventricular and periventricular hemorrhages, especially in the germinal matrix [20] [41].

It is therefore important to ensure that immediate care of extremely preterm neonates avoids interventions which could provoke such fluctuations in systemic blood pressure. This specifically includes cord milking carried out with the notional idea of providing the neonate an “extra volume of blood.”

In 2019, Katheria et al. published a study in which milking of the umbilical cord four times was compared with deferred cord clamping in 540 infants with gestational ages ranging from 23 to 31 GW [56]. The primary study outcome “death or severe cerebral hemorrhage” did not differ significantly between groups (cord milking: 29/236 [12%] vs. deferred cord clamping: 20/238 [8%]; risk difference 4% [95% CI] −2%–9%; P = 0.16). But the rate of severe cerebral hemorrhage in the subgroup of neonates born at 23–27 GW after umbilical cord milking was almost four times higher compared to the group with deferred cord clamping (cord milking: 20/93 [22%] vs. deferred cord clamping: 5/89 [6%]; risk difference 16% [95% CI] 6%–26%; P = 0.002). These differences were no longer observed in older neonates (28+0–31+6 GW) ([Table 2]), although the statistical power was insufficient to definitively resolve this issue [56].

Table 2 Rate of severe cerebral hemorrhage in preterm infants born from 23 + 0 to 31 + 6 GW after milking of the umbilical cord compared with infants treated with deferred cord clamping. Data from: [56].

Gestational age (GW)	Cord milking	Deferred cord clamping	Risk difference (%)	P value	P value for interaction
	Severe cerebral hemorrhage grade III–IV (N)
23+0–31+6	20/236 (8%)	8/238 (3%)	5 (1–9)	0.02
23+0–27+6	20/93 (22%)	5/89 (6%)	16 (6–26)	0.002	0,003
28+0–31+6	0/143 (0%)	3/149 (2%)	−2 (−4–1)	0.24

The medical professionals responded quickly to these data. So-called “birth trolleys” were developed which permit deferred cord clamping at the time of delivery even for extremely preterm neonates and still allow immediate neonatal care to be provided. Deferred cord clamping should always be preferred for preterm infants as it permits physiological transition of the cardiovascular system from the intrauterine to the postnatal phase [57] [58]. A “vent first” strategy is key, i.e., the cord should not be clamped before the lungs have inflated [59].

Hypothermia

The use of mild hypothermia (33°C core body temperature) over a period of 72 hours to treat asphyctic term-born infants is now clinical standard. Six randomized studies on this topic were published between 2005 und 2011. The results of these studies were summarized in a meta-analysis published in 2013 [60]. A total of 1344 children were included. The primary outcome “death or major neurodevelopment disability at the age of 18–22 months” was reduced by 25% (RR 0.75, 95% CI 0.68–0.83). The number needed to treat was seven [60].

What was not clear was whether preterm infants would also benefit from this intervention. It was not possible to rule out that the typical complications of premature neonates such as cerebral hemorrhage, necrotizing enterocolitis, or coagulation disorders might be exacerbated by mild hypothermia. For this reason, the Eunice Kennedy Shriver NICHD initiated a prospective randomized study which included 168 preterm infants born in 19 perinatal centers in the USA between 2015 and 2022. Infants showing signs of neonatal encephalopathy were recruited into the study. Encephalopathy was clinically diagnosed using the Thompson score and was a risk factor for the development of hypoxic-ischemic brain damage. Infants with a birth weight of < 1500 g, malformations, or a body temperature of < 34°C were excluded. Core body temperature was lowered to 33.5°C for 72 h in the intervention group [61].

The primary study outcome “death or moderate/severe neurodevelopment disability at the age of 18–22 months” affected 29 out of 83 infants (35%) in the intervention group and 20 of 69 infants (29%) in the control arm (RR 1.11, 95% CI 0.74–2.00). The probability of harm by hypothermia was 74% ([Table 3]). When stratified by gestational age, the incidence of the primary study outcome was higher in the hypothermia group for every week of gestation [61].

Table 3 Use of mild hypothermia in preterm infants born 33+0–35+6 GW with neonatal encephalopathy.

	Hypothermia		Normothermia
	n/N	%	n/N	%	RR (95% CI)	Probability of harm
Preterm infants born between 33 + 0 and 35 + 6 GW with neonatal encephalopathy were recruited. Core body temperature was lowered to 33.5 °C for 72 h in the intervention group. 95% CI = 95% confidence interval; RR = relative risk. Data from: [61]
Death or moderate or severe disability	29/83	35	20/69	29	1.11 (0.74–2.00)	74%
Death	18/83	22	9/69	13	1.38 (0.79–2.85)	87%
Survival with moderate or severe disability	11/83	13	11/69	16	0.86 (0.46–1.63)	32%

Mortality alone was 22% in the intervention group and 13% in the control group (RR 1.38, 95% CI 0.79–2.85). The probability of harm by hypothermia was 87% ([Table 3]). No differences in known side effects of hypothermia (cardiac arrhythmia, persistent metabolic acidosis, severe bleeding, skin lesions) were observed. Hyperglycemia was observed more often but the difference was not significant (23 vs. 12%) (RR 1.64, 95% CI 0.92–3.27) [61].

Mild hypothermia does not reduce mortality or the rate of moderate/severe neurodevelopmental disability at the age of 18–22 months in preterm infants. On the contrary, this intervention in preterm infants causes additional harm [61]. It is possible that hypothermia-induced hyperglycemia plays a role in this. Studies show that elevated glucose levels may exacerbate hypoxic-ischemic brain damage [62].

Neuroprotective Strategies in the Secondary and Tertiary Phase

As secondary and tertiary cell damage can occur days or even weeks after the primary insult due to persistent inflammation and lack of trophic stimulation ([Fig. 1]) [12] [63], in addition to providing preterm infants with the best possible initial care, it is necessary to optimize the subsequent care provided in the intensive care unit.

Clinical measures

The aim of primary care provided to very preterm neonates is to avoid high fluctuations in CO₂, blood pressure, and temperature [64] [65] [66]. If possible, invasive ventilation should not be used initially. The less invasive surfactant administration (LISA) method has proven to be very useful [67]. It is also important to prevent acidosis [68]. The head should be placed in a neutral midline position [69] and painful interventions should be minimized [70]. Balanced electrolyte levels are important, especially serum sodium concentrations [71].

As the most recent studies have shown, implementing appropriate standard operating procedures which include the above-listed measures reduces perinatal brain damage rates and improves the long-term neurological development of these children [72] [73] [74] [75] [76]. In addition to acute care, further measures may promote neuroplasticity and psychomotor maturation of the infants and thereby counter secondary and tertiary cell damage [8]. Such measures include early skin-to-skin contact (kangaroo care) [77] [78], avoiding strong light and loud acoustic stimuli [79], positive stimulating sounds [80], reinforcing good physiological neonatal sleep-wake cycles [81], family-centered care [82], parental voices with parents talking to their children [81] [83], and positive reinforcement of social interactions [84]. Breastfeeding and breast milk intake play an especially important role.

Breastfeeding and breast milk intake

Breast milk provides neonates with the appropriate physiological nutrition and is therefore recommended for all neonates. It is associated with numerous positive effects on the child’s short-term and long-term health (protection against infections, decreased incidence of metabolic syndrome disorders) and with better neurocognitive development.

For mothers of preterm born infants, initiating and maintaining lactation during the transition to breastfeeding presents specific challenges which can mean that preterm infants have a high risk of not being fed with their own mother’s milk and subsequently not being breastfed.

Numerous retrospective comparative studies have confirmed that being fed with breast milk obtained from the infant’s own mother and breastfeeding are associated with better neurological outcomes in preterm infants [85] [86] [87] [88] [89]. A joint analysis of two population-based French studies [89] showed that despite suboptimal initial weight gain, breastfed children showed better cognitive development at the age of five years.

The underlying mechanisms have been discussed a lot. It has often been pointed out that there is an association between breastfeeding and socioeconomic status, which in turn may determine the neurological outcome. However, the observed effect of breastfeeding remains, even after adjustment for socioeconomic factors.

Although breastfeeding is associated with greater focus by the mother on the infant which could be a partial explanation for the positive developmental effect, a number of different substances have been identified in human breast milk in recent years which could have an impact on brain development, for example, lactoferrin, various growth factors, cytokines [90], extracellular vesicles [91] [92], and even live cells, including stem cells [93]. In fact, in addition to the effects of breast milk intake and breastfeeding on functional parameters such as IQ and motor skills, morphological differences in brain architecture between breast milk-fed infants and formula-fed infants have been identified [94] [95] [96], which are ascribed to the impact of these components.

Feeding infants with breast milk also supports development of a healthy microbiome, which contributes to optimal development.

Interestingly, donor breast milk is not superior to formula if it is used to supplement breast milk from the infant’s own mother [97]. This is due, on the one hand, to changes in the composition of maternal breast milk, which changes and adapts to the infant’s gestational age and the child’s respective needs over the course of lactation [98] and, on the other hand, due to the fact that donor milk is subjected to various types of treatment such as refrigeration, freezing or pasteurization, which change the biological properties of the milk [99].

The way in which breast milk is administered also has a non-negligible impact on its biological effects. During breastfeeding, the physiological form of ingesting nutrition, the mucosa of the entire mouth, nose and throat comes into contact with breast milk. This has immunological impacts. Some substances may reach the brain transnasally. It is therefore recommended to combine tube feeding of breast milk in very and extremely preterm infants with the administration of small oral amounts [100]. Initial observations have also indicated that the nasal administration of maternal breast milk could have a therapeutic effect after perinatal brain damage [101] [102] [103] [104].

Promoting breastfeeding in the secondary and tertiary phase is therefore a very important neuroprotective measure.

Experimental approaches

Some inflammation-inhibiting interventions to minimize secondary and tertiary cell damage have already been investigated in animal experiments. For example, intracerebroventricular injection of the TNF inhibitor etanercept on days 3, 8 and 13 after umbilical occlusion significantly reduced induced brain damage in the white matter of immature ovine fetuses. It was also associated with improved maturation of oligodendrocytes and increased myelination [105].

Erythropoietin, an endogenous growth factor with anti-inflammatory, anti-excitotoxic and anti-apoptotic properties, has also been shown to have neuroprotective effects. Unfortunately, the findings of the five clinical studies carried out to date are inconsistent [106] [107] [108] [109] [110]. The two biggest studies did not find that erythropoietin administered to very preterm infants (24–32 GW) had any effect on neurological development at the age of two years [108] [110].

Melatonin is another potential candidate for neuroprotection. This naturally occurring indolamine is released from the epiphysis and regulates the circadian rhythm [111]. Melatonin crosses the placenta and the blood-brain barrier and is a known antioxidant [111]. A neuroprotective effect on hypoxic-ischemic and inflammatory brain damage has been observed in experimental studies [112]. In a prospective randomized study in preterm infants, lower lipid peroxidation was noted after the administration of melatonin in the first 21 days of life [113]. Further investigations into dosages and the timing of administration are planned in preclinical studies [114].

Caffeine, which is used clinically as a respiratory stimulant for preterm infants, is also being discussed as a potential neuroprotective agent [115]. Caffeine is an adenosine receptor antagonist with anti-inflammatory properties. In a cerebral ischemia/hypoxia model in neonatal rodents, caffeine was found to reduce induced brain damage and improved myelination and maturation of oligodendrocytes [116] [117] [118] [119]. In a prospective randomized study, infants with a birth weight < 1250 g who received caffeine for apnea had lower rates of cerebral palsy at the age of 18–21 months (4.4% vs. 7.3%; aOR 0.58, 95% CI 0.39–0.87) and neurological developmental delay (33.8 vs. 38.3%; aOR 0.81, 95% CI 0.66–0.99) [120].

Secondary and tertiary cell damage has been observed to occur days or even weeks after a cerebral perinatal insult due to insufficient trophic stimulation [12] [63]. In recent years interest has focused on the potential uses of pluripotent stem cells. These stem cells activate angiogenesis, neurogenesis, synaptogenesis, and neuronal networking. A meta-analysis of experimental studies in neonatal rodents showed that the use of neuronal stem cells can reduce the extent of infarction and significantly improve motor and cognitive functioning [121]. Unfortunately, there are currently only a few clinical phase I/II studies on this topic. Moreover, these studies mainly focus on chronic diseases rather than perinatal insults [122]. A study of preterm infants < 28 GW to investigate safety and viability after administering autologous mononuclear stem cells obtained from umbilical cord blood has been initiated [123].

Conclusion

Cerebral morbidity rates continue to be high in very preterm infants and significantly define the long-term morbidity of these infants. To offer these children an optimal start in life, it is very important that they are cared for in a level I perinatal center right from the start. There are also a number of perinatal measures which can significantly improve the neuronal development of preterm infants. They include the use of antenatal steroids, magnesium sulfate, and deferred cord clamping. As secondary and tertiary cell damage can occur days or even weeks after the primary insult due to persistent inflammation and lack of trophic stimulation, in addition to providing preterm infants with the best possible initial care, it is also necessary to optimize subsequent care in the intensive care unit in terms of providing a neuronal-positive stimulating environment. This includes early skin-to-skin contact (kangaroo care), avoiding strong light and loud acoustic stimuli, positive stimulating sounds, strengthening neonatal physiological sleep-wake cycles, providing family-centered care, parents talking to their infant, and positive strengthening of social interactions. Breastfeeding and feeding with breast milk are particularly important in this context.

Conflict of Interest

The authors declare that they have no conflict of interest.

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Publication History

Received: 23 January 2025

Accepted after revision: 12 March 2025

Article published online:
30 June 2025