The rate of human brain growth is greatest in mid-to-late fetal gestation, corresponding to peak neuronal dendritogenesis. In pregnancies complicated by fetal growth restriction (FGR) caused by placental dysfunction, brain development is adversely impacted, with evidence of reduced total and hippocampal brain volume in childhood and cognitive deficits. The cellular basis for hippocampal maldevelopment and dysfunction in FGR is unknown. In this study we employed complementary preclinical and clinical investigations of hippocampal developmental trajectory in growth restricted neonates to address this knowledge gap. In the preclinical study (FGR n=18, control n=19), FGR was induced in fetal sheep via surgical induction of placental insufficiency at 89 days gestational age (dGA, term is 148dGA), and after near-term birth (136dGA), postnatal memory function was measured over four weeks. Neuronal dendritogenesis (dendrite length, branching, complexity) was assessed using Golgi-Cox staining of individual hippocampal Cornu Ammonis (CA)1 neurons at two neonatal timepoints, newborn age at 24 hours after birth and 4-weeks of age, to compare the trajectory of hippocampal neuron development in FGR and control lambs. Results show that, in control lambs, total dendrite length and branching of CA1 hippocampal neurons significantly increased between newborn age and 4-weeks. In FGR lamb brains, neither dendrite length or branching increased over this period, and dendrite deficits were worse in FGR lambs at 4-weeks, corresponding to reduced hippocampal area. In 4-week-old lambs, we observed a significant correlation between total dendrite length of CA1 neurons and memory function. Hippocampal growth trajectory and function deficits were corroborated in small for gestational age (SGA) infants born very preterm. Magnetic resonance imaging (MRI) was performed in very preterm infants in early life, and repeated at term equivalent age, showing that the trajectory of anterior hippocampal growth was significantly reduced in SGA infants (n=20) compared to appropriate for gestational age (AGA; n=139) infants. Within the SGA infant cohort, reduced anterior hippocampal volume was significantly associated with lower Bayley Cognitive Composite scores at 18 months corrected age, controlling for gestational age at birth and infant sex. Together, these findings demonstrate that the trajectory of hippocampal growth is significantly impaired in SGA/FGR infants, caused by disturbed neuronal dendritogenesis that is programmed by an adverse fetal environment and persists, or worsens, after birth. Results in the clinical cohort provide the critical link between programming of reduced dendritogenesis, hippocampal volume deficit and cognitive dysfunction in SGA infants.

Fetal hypoxaemia during pregnancy is not uncommon, arising from chronic placental insufficiency or acute stressors. In the case of placental insufficiency and chronic fetal hypoxia, fetal growth is reduced, resulting in fetal growth restriction (FGR). Fetal hypoxaemia initiates an immediate adaptive strategy to preserve brain oxygen delivery - the brain sparing response. Asymmetric FGR, in which head size is relatively larger than body size, is evidence of prolonged brain sparing. The acute physiology of the brain sparing response is well-defined in preclinical studies, involving peripheral vasoconstriction and reduced cerebral resistance to promote cerebral vasodilatation. Yet, the mechanisms that maintain fetal brain sparing during sustained hypoxaemia remain incompletely understood. Furthermore, although brain sparing has historically been interpreted as protective, this concept is being challenged, with its presence linked to increased risk of death or neonatal morbidity and neuropathology. This contradiction reflects that brain sparing is not static but evolves with the severity of fetal hypoxaemia; clinical evidence points to a front-to-back pattern of brain vasodilatation that initially prioritises cortical perfusion for higher-order function, whereas prolonged or severe hypoxaemia drives a shift towards brainstem preservation and survival. Thus, the brain sparing response is initiated by fetal hypoxaemia and is a unique indicator of fetal compromise, but it progresses from a compensatory to a maladaptive response. The mechanisms, multisystem physiology and ontogeny of sustained brain sparing in severe FGR are not well characterised, but advancing this knowledge affords new opportunities to diagnose and manage FGR, and to intervene to prevent adverse consequences.

The last pregnancy trimester is critical for fetal brain development but is a vulnerable period if the pregnancy is compromised by fetal growth restriction (FGR). The impact of FGR on the maturational development of neuronal morphology is not known, however, studies in fetal sheep allow longitudinal analysis in a long gestation species. Here we compared hippocampal neuron dendritogenesis in FGR and control fetal sheep at three timepoints equivalent to the third trimester of pregnancy, complemented by magnetic resonance image for brain volume, and electrophysiology for synaptic function. We hypothesized that the trajectory of hippocampal neuronal dendrite outgrowth would be decreased in the growth-restricted fetus, with implications for hippocampal volume, connectivity, and function. In control animals, total dendrite length increased with advancing gestation, but not in FGR, resulting in a significantly reduced trajectory of dendrite outgrowth in FGR fetuses for total length, branching, and complexity. Ex vivo electrophysiology analysis shows that paired-pulse facilitation was reduced in FGR compared to controls for cornu ammonis 1 hippocampal outputs, reflecting synaptic dysfunction. Hippocampal brain-derived neurotrophic factor density decreased over late gestation in FGR fetuses but not in controls. This study reveals that FGR is associated with a significant deviation in the trajectory of dendrite outgrowth of hippocampal neurons. Where dendrite length significantly increased over the third trimester of pregnancy in control brains, there was no corresponding increase over time in FGR brains, and the trajectory of dendrite outgrowth in FGR offspring was significantly reduced compared to controls. Reduced hippocampal dendritogenesis in FGR offspring has severe implications for the development of hippocampal connectivity and long-term function.

BACKGROUND:Chronic hypoxemia is a common cause of fetal growth restriction and can have significant effects on the developing fetal lung. Maternal antioxidant treatment in hypoxic pregnancy protects against offspring cardiovascular dysfunction. The effects of antenatal antioxidants on lung development in the chronically hypoxic growth restricted fetus is unknown. METHODS:We investigated the effect of maternal daily Vitamin C (200 mg/kg i.v. vs. Saline) for a month in late gestation on molecular markers regulating lung maturation between normoxic normally grown and hypoxic growth-restricted fetal sheep. Chronic fetal hypoxia and fetal growth restriction were induced by exposure to maternal chronic hypoxia (10% O2 vs. Normoxia=21% O2) from 105-138 d gestation (term=145 d). RESULTS:The data show a differential effect of antenatal Vitamin C treatment on regulation of genes involved in surfactant maturation, sodium movement and hypoxia signaling. Limited responsiveness to antenatal Vitamin C exposure in the lung of the hypoxic fetus, compared to responsiveness to antenatal Vitamin C in the normoxic fetus, suggests a maximal upregulation of the molecular signaling pathways in response to the chronic hypoxic insult alone. CONCLUSION:We provide molecular insight into the heterogeneity of antenatal Vitamin C treatment on development of the normoxic and growth restricted hypoxic fetal lung. IMPACT:The effect of maternal Vitamin C on molecular markers of lung maturation between normoxic normally grown and hypoxic growth restricted fetal sheep was unknown. We show a differential effect of Vitamin C with a greater increase in molecular markers of lung maturation in normoxic compared with hypoxic fetuses. Limited responsiveness in the hypoxic fetal lung is likely due to maximal upregulation by the hypoxic insult alone, thus added exposure to Vitamin C is unable to upregulate the system further. The work highlights the need to understand differential effects of antenatal interventions in healthy and complicated pregnancy, prior to clinical translation.

Fetal growth restriction (FGR) increases the risk of cardiovascular disease. FGR is linked to placental insufficiency and fetal hypoxemia, leading to oxidative stress and inflammation, which collectively influence the developmental programming of cardiovascular disease. This study assessed whether melatonin (MLT), a potent antioxidant and anti-inflammatory agent, could prevent cardiovascular deficits associated with FGR. Placental insufficiency was induced in ewes at 89 days of gestational age (dGA, term 148 dGA). Ewes were randomly allocated to control, FGR or FGR+MLT (i.v., 15 mg day-1, from 95 dGA to birth) groups. Lambs were delivered preterm at 136 dGA and assessed as newborn (24 h) and 4-week-old lambs. Vascular function was determined in femoral arteries using in vitro wire myography and vascular morphology as assessed in carotid and femoral arteries. Newborn FGR lambs were ∼30% smaller than control lambs with an increased brain-to-body weight ratio, indicative of brain sparing. Femoral endothelial function declined between ∼24 h after birth and 4 weeks in FGR lambs. By contrast, femoral arteries from newborn FGR+MLT lambs displayed transient endothelial dysfunction that improved by 4 weeks. However, these arteries showed elevated levels of oxidative stress and inflammation. Despite improving endothelial function, melatonin also disrupted the brain-sparing response in FGR lambs. Furthermore, by 4 weeks of age, melatonin treatment led to heightened oxidative stress and inflammatory markers in the peripheral vasculature, suggesting a potential trade-off between vascular benefits and systemic maladaptation. These findings highlight the complexity of melatonin's effects on the cardiovascular system and underscore the need for careful evaluation of its long-term safety and efficacy before clinical translation. KEY POINTS: Fetal growth restriction (FGR) significantly increases the lifelong risk of cardiovascular disease, and there are currently no targeted treatments to mitigate these risks. This study follows growth-restricted lambs from birth to 4 weeks of age (comparable to a 1-year-old human in terms of cardiovascular function) to characterise how FGR affects vascular development over time. FGR lambs exhibited progressive endothelial dysfunction in the femoral artery, but antenatal melatonin treatment restored endothelial function long-term despite the presence of vascular oxidative stress and inflammation. The brain-sparing response is a key adaptive mechanism for fetal survival, yet melatonin appears to dampen this response, highlighting the need for further investigation into its broader physiological effects.

BACKGROUND:Preterm brain injury involves persistent inflammation, making it a potential therapeutic target. Current large animal models focus on short-term outcomes, limiting understanding of long-term effects. We developed an ovine model of inflammation-induced preterm brain injury to assess long-term neuropathology at an age equivalent to early cerebral palsy diagnosis in human infants. METHODS:Fetal sheep were instrumented at gestational day (d) 90-91 (term is 148d): one group received lipopolysaccharide (LPS 200 ng; n = 9) on 96d, 97d, and 98d (0.65 gestation, ∼25-26 weeks human brain development), and a control group received saline (n = 8). Birth was induced on 138d, and lambs were euthanised within 24 h of birth. Brains were evaluated for white matter injury, microglial/macrophage activation and astrogliosis in the subcortical (SCWM), periventricular (PVWM), and cortical (CWM) white matter, subventricular zone (SVZ), and corpus callosum (CC). RESULTS:Antenatal LPS administration was associated with significant persistent microglial/macrophage activation in the PVWM (P = 0.04), SCWM (P = 0.01), and CWM (P = 0.006). Furthermore, LPS exposure was associated with reduced oligodendrocyte cell number in the PVWM (P = 0.02), SCWM (P = 0.001), and CWM (P = 0.0001), and reduced myelination in CWM (CNPase, P < 0.0001 and MBP, P = 0.04) and SVZ (MBP, P = 0.05). No difference in astrogliosis or microhaemorrhages was observed. CONCLUSION:We demonstrated that in a large animal model of inflammation-induced intrauterine preterm brain injury, long-term persistent inflammation occurs, along with significant white matter injury, including loss of oligodendrocytes and reduced myelination in multiple white matter regions. This model paves the way for long-term evaluation of promising therapeutics and behavioral assessment in this clinically relevant model of persistent preterm brain injury.

Fetal growth restriction (FGR) arises from chronic hypoxia and increases the risk of cardiovascular dysfunction following perinatal asphyxia, although underlying mechanisms remain unclear. We investigated whether cardiovascular responses to asphyxia are impaired in preterm FGR lambs and whether this arises from α1- and β1-adrenergic receptor dysfunction. Ewes underwent sterile fetal surgery at 89 days’ gestation (d; term=148 d) to induce FGR (single umbilical artery ligation) or sham surgery (control). At 126 d, lambs were delivered, instrumented and randomised to immediate ventilation (ControlVENTn=6; FGRVENTn=6) or asphyxia (ControlASPHYXIAn=12; FGRASPHYXIAn=11) by umbilical cord occlusion until diastolic blood pressure (BP) decreased to 10 mmHg. Lambs were ventilated for 8 hours before baseline ex vivo cardiac function was assessed via Langendorff perfusion to measure left ventricular developed pressure (LVDP), heart rate (HR) and coronary perfusion pressure (CPP). Ex vivo α1- and β1-adrenergic responses were assessed via phenylephrine and dobutamine administration, respectively. FGRASPHYXIA lambs had lower BP during asphyxia and took longer to reach a diastolic BP of 10 mmHg (P<0.05 vs ControlASPHYXIA). FGRASPHYXIA lambs had lower BP in the first 5 minutes after return of spontaneous circulation due to impaired vascular contractility (P<0.05 vs ControlASPHYXIA). Baseline LVDP, HR and CPP were similar between groups. FGRASPHYXIA lambs had increased LVDP responses to phenylephrine and dobutamine (P<0.05 vs FGRVENT and ControlASPHYXIA), without significant changes to HR or CPP. Overall, FGR lambs exhibit impaired vascular contractility and heightened cardiac α1- and β1-adrenergic responsiveness after perinatal asphyxia, consistent with reduced autonomic regulation, potentially increasing susceptibility to cardiovascular dysfunction postnatally.

Antenatal inflammation/infection is a major cause of neonatal apnoea and hypoventilation. Prostaglandin E2 (PGE2) is a key inflammatory mediator associated with depression of fetal and neonatal breathing. We aimed to determine whether antenatal ibuprofen, a cyclooxygenase inhibitor that reduces synthesis of PGE2, restores fetal breathing movements (FBM) in late-gestation fetal sheep exposed to systemic lipopolysaccharide (LPS). Fetal sheep (125 days gestation, d; term ~148 d) were instrumentally monitored for continuous measurement of FBM and physiological parameters. At 130 d fetuses were randomly allocated between groups receiving i.v. saline (CTLSAL, n = 9), escalating doses of LPS (i.v.) over 3 days (LPSSAL, n = 8), or ibuprofen one hour after each LPS dose (LPSIBU, n = 8). Regular plasma samples were collected for PGE2 assessment. At 135 d, cerebrospinal fluid and brainstem tissue were collected at autopsy for assessments of PGE2 expression, and immunohistochemical quantification of astrocytes and microglia within key brainstem respiratory centres was performed to assess inflammation. LPS exposure increased PGE2 levels in plasma, cerebrospinal fluid and the RTN/pFRG (p < 0.05) and decreased the incidence, amplitude and amount of the accentuated (>5 mmHg) FBMs. Ibuprofen reduced plasma and RTN/pFRG PGE2 expression (p < 0.01 and p = 0.031, respectively) but did not restore FBMs. Astrocyte and microglial density increased in the RTN/pFRG, NTS and raphe nucleus in LPSIBU fetuses, compared to LPSSAL (p < 0.05). Antenatal ibuprofen treatment did not restore depressed FBM, despite reducing the circulating and brainstem PGE2 levels in LPS-exposed fetal sheep. Other inflammatory pathways or more specific targeting of PGE2 may be more effective in preventing apnoea caused by exposure to intrauterine infection/inflammation.

Introduction Fetal growth restriction (FGR) arises from chronic hypoxia and increases the risk of cardiovascular dysfunction following perinatal asphyxia, although the underlying mechanisms are unknown. We investigated whether FGR lambs have altered cardiovascular responses to perinatal asphyxia compared to control lambs, and whether impairments in α1 and β1 adrenergic receptor function underlie these responses. Methods Single or twin-bearing ewes underwent sterile fetal surgery at 89 days gestation (dGA; term=148d) to induce FGR (single umbilical artery ligation) or sham surgery (Control). At 126dGA, lambs were delivered via caesarean section, instrumented and randomised to immediate ventilation (ControlVENT n =6; FGRVENT n =6), or asphyxia (ControlASPHYXIA n =12; FGRASPHYXIA n =11) induced by umbilical cord occlusion while withholding resuscitation until diastolic blood pressure (BP) decreased to 10mmHg. Lambs were ventilated for 8 hours before baseline ex vivo cardiac function was assessed via Langendorff perfusion to measure left ventricular developed pressure (LVDP), heart rate (HR) and coronary perfusion pressure (CPP). Ex vivo α1 and β1 adrenergic responses were assessed via phenylephrine (10−5 to 10−2 mmol/L) and dobutamine (10−7 to 10−4) administration, respectively. Results FGRASPHYXIA lambs had lower BP during asphyxia (p<0.05 vs ControlASPHYXIA) and took longer to reach a diastolic BP of 10mmHg (14.5 ± 0.8 min vs. 19.2 ± 1.3 min; p=0.005). FGRASPHYXIA lambs had lower BP in the first 5 minutes after return of spontaneous circulation (p<0.05) due to impaired vascular contractility, with reduced Tau, dP/dtmax and dP/dtmin (p<0.03 vs ControlASPHYXIA). Baseline LVDP, HR and CPP were similar between groups, however FGRASPHYXIA lambs had increased LVDP responses to phenylephrine and dobutamine (p<0.05 vs ControlASPHYXIA), without significant changes to HR or CPP. Conclusion FGR lambs have altered physiological responses to perinatal asphyxia due to impaired vascular contractility and dysregulated cardiac α1 and β1 adrenergic receptor function, which may increase susceptibility to cardiovascular dysfunction in the neonatal period. ### Competing Interest Statement The authors have declared no competing interest.

More than 1 in 10 babies are compromised by preterm birth, low birthweight, maternal pregnancy complications or perinatal hypoxia-ischemia, leading to death or lifelong disability. Advancements in pregnancy and newborn care to date have been underpinned by mechanistic and physiological insights from fundamental discovery science. However, there are growing challenges to the perinatal research pipeline that threaten the next breakthroughs. Reduced funding, discipline-specific publishing, and high attrition are reducing pipeline research capacity and particularly large animal research; over the last two decades there has been a 12.6% decrease in the number of institutes that conduct large animal perinatal studies. Furthermore, paradoxically, over-prioritisation of translational research has come at the expense of discovery science. The complexity of fetal and newborn physiology, transition at birth, pathophysiology, multi-hit and multi-organ insults, and the progressive nature of development and injury, mean that the fetus and newborn are unique study subjects. The fetus and newborn are not small adults. Consequently, progression to clinical trials must acknowledge all available evidence provided through preclinical and clinical discoveries prior to adopting new interventions. The next critical innovations towards a healthy start to life need a thriving perinatal research pipeline that values and prioritises discovery evidence. IMPACT: Ensuring a healthy start to life for all infants needs new discoveries. But there are growing challenges to the perinatal research pipeline that threaten the next advances. Poor funding, competitive publishing, and high attrition are reducing discovery research capacity and reducing large animal research. The unique physiology and ongoing organ development in the fetus and neonate means that they are not small adults, and we must support the perinatal research pipeline to accumulate gold-standard evidence that will inform the next successful advances for better newborn health.

Preterm newborns exposed to infection/inflammation in utero are at an increased risk of requiring respiratory support at birth, often in the form of mechanical ventilation. Mechanical ventilation and intrauterine inflammation independently cause inflammation in brainstem respiratory-related centres. However, the synergistic effect of intrauterine inflammation and mechanical ventilation on brainstem inflammation is unknown. We hypothesized that 24 h of mechanical ventilation after intratracheal LPS exposure exacerbates inflammation in the brainstem respiratory-related centres of preterm foetal sheep. Preterm foetal sheep (110 ± 1 days' gestation) were surgically instrumented with catheters and tubing for in utero ventilation (VENT). At 115 ± 3 days, foetal sheep were randomly assigned to: (i) unventilated control + intratracheal (i.t.) saline (CONTSAL; n = 6), (ii) 24 h of VENT with i.t. saline (VENTSAL; n = 7), (iii) unventilated control with i.t. LPS (CONTLPS; n = 7) or (iv) 24 h VENT with i.t. LPS (VENTLPS; n = 6). In utero ventilation was started 1 h after i.t. LPS/saline administration, targeting a tidal volume of 3-5 mL/kg for 24 h. Serial plasma samples and post-mortem CSF were assessed for systemic and central inflammation, respectively. At 24 h, brainstem tissue was collected for molecular and histological assessment of markers of inflammation and injury. Plasma interleukin (IL)-1β, IL-6, IL-10 and interferon-γ-induced protein-10 (IP-10) were significantly increased in VENTLPS foetuses compared to CONTSAL and VENTSAL (P < 0.05). IL-6 was higher in the cerebrospinal fluid of VENTLPS groups compared to CONTLPS (P = 0.0002). mRNA tumour necrosis factor (TNF) (P = 0.035) and prostaglandin-endoperoxide synthase-2 (PTGS2) (P = 0.011) were increased in the brainstems of VENTLPS foetuses compared to CONTLPS. LPS exposure increased the number of astrocytes, microglia and STAT3+ cells within key respiratory-related centres compared to CONTSAL and VENTSAL (P < 0.01). Mechanical ventilation for 24 h after i.t. LPS amplifies markers of systemic and brainstem inflammation but does not further exacerbate histological inflammation or cell death in brainstem respiratory-related centres. The exacerbated inflammation suggests that mechanical ventilation preceded by intrauterine inflammation may impede cardiorespiratory control with adverse effects on spontaneous breathing and cardiovascular function in preterm infants.

The cardiopulmonary transition at birth is a critical physiological process requiring coordinated cardiovascular adaptation to meet the increased circulatory demands of extrauterine life. This transition may be compromised in infants affected by suboptimal fetal growth, such as in infants born small for gestational age (SGA) or classified with fetal growth restriction (FGR). Suboptimal fetal growth often arises from reduced oxygen and nutrient supply, leading to prioritised perfusion of crucial organs and subsequent cardiac and arterial remodelling. These cardiovascular adaptations, while necessary for fetal survival, may persist postnatally and increase the risk of an impaired cardiovascular transition at birth. Altered echocardiographic function and cardiac injury biomarkers are often detectable in this population during the early postnatal period, indicating underlying myocardial stress and a predisposition to an impaired transition. FGR and/or SGA neonates often exhibit impaired diastolic function, reflecting impaired myocardial relaxation and reduced compliance, and systolic dysfunction, including a reduced capacity to increase left ventricular output over time. Additionally, elevated pulmonary vascular resistance contributes to an increased risk of respiratory morbidity. Emerging preclinical data suggest that these adaptations may impede the neonate's ability to respond to perinatal stressors, thus increasing the risk of adverse outcomes. Understanding the multifaceted nature of cardiovascular dysfunction in FGR and/or SGA infants during the perinatal period is essential to improving their long-term outcomes, thus reducing the risk of cardiovascular disease later in life.

IntroductionChronic fetal hypoxia is commonly associated with fetal growth restriction and can predispose to respiratory disease at birth and in later life. Antenatal antioxidant treatment has been investigated to overcome the effects of oxidative stress in utero to improve respiratory outcomes. We aimed to determine if the effects of chronic fetal hypoxia and antenatal antioxidant administration persist in the lung in early adulthood.MethodsChronically catheterised pregnant sheep were exposed to normoxia (N; n = 20) or hypoxia (H; n = 18; 10% O2) ± maternal daily i. v. saline (N = 11; H = 8) or Vitamin C (VC; NVC = 9; HVC = 10) from 105 to 138 days (term, ∼145 days). Lungs were collected from female lambs 9 months after birth (early adulthood). Lung tissue expression of genes and proteins regulating oxidative stress, mitochondrial function, hypoxia signalling, glucocorticoid signalling, surfactant maturation, inflammation and airway remodelling were measured.ResultsChronic fetal hypoxia upregulated lung expression of markers of prooxidant, surfactant lipid transport and airway remodelling pathways in early adulthood. Antenatal Vitamin C normalized prooxidant and airway remodelling markers, increased endogenous antioxidant, vasodilator and inflammatory markers, and altered regulation of hypoxia signalling and glucocorticoid availability.ConclusionThere are differential effects of antenatal Vitamin C on molecular markers in the lungs of female lambs from normoxic and hypoxic pregnancy in early adulthood.

BACKGROUND:Intraventricular haemorrhage (IVH) is the primary neuropathology in infants born very preterm. IVH describes bleeding into the ventricular space of the newborn brain, originating from the germinal matrix, termed germinal matrix haemorrhage. IVH is diagnosed at a rate of 1 in 5 infants born very preterm (less than 32 weeks' gestation), but the incidence increases with earlier gestation at birth. IVH is graded in severity (I to IV), and the neurological sequelae of IVH in infants born very preterm are significant, with more than 1 in 4 infants with any grade of IVH subsequently diagnosed with a moderate to severe neurodevelopmental deficit, increasing to more than half of infants diagnosed with severe IVH (grade III/IV). SUMMARY:The high susceptibility to IVH in infants born at less than 32 weeks' arises in part to the presence of the germinal matrix. The germinal matrix is a transient brain region that produces neural stem and progenitor cells. The germinal matrix region is rich in angiogenic blood vessels that have a low density of pericyte and astrocyte coverage to provide structural stability, and it is a border zone for vascular endpoints that are highly fragile to haemodynamic instability. In addition to immaturity, antenatal complications may also adversely impact cerebrovascular development, pericyte and astrocyte coverage, and subsequently the structural integrity of the blood-brain barrier that might increase the risk for IVH. KEY MESSAGES:Here, we will report the maturational profile of cerebrovascular development in the extremely preterm neonate, and implications for susceptibility to IVH, the complications that may contribute to the risk of haemorrhage, and neurodevelopmental deficits that primarily arise from IVH. We aimed to elucidate the cellular foundations of IVH to provide insight into neuroprotective targets.

Within 24 h of birth, growth-restricted (FGR) newborn lambs exhibited altered lipid and serotonin metabolites, suggesting disrupted postnatal cardiac metabolic adaptation. Despite upregulation of the fatty acid transporter gene SLC27A6, with other fatty acid oxidation genes remaining largely unchanged, reductions in lipid and carnitine metabolites indicate potential impairments in fatty acid utilization. Decreased serotonin bioavailability further suggests metabolic reprogramming in FGR hearts, highlighting the need for future studies on the implications for postnatal cardiac function.

BACKGROUND: Intraventricular hemorrhage (IVH) most commonly occurs in infants born very preterm (<32 weeks' gestation). There are mixed findings on whether infants small for gestational age (SGA) or with suspected fetal growth restriction (FGR) are at higher risk for IVH. Understanding the relationship between SGA or FGR and IVH is critical to inform clinical care. OBJECTIVE: The primary aim was to determine the rates of IVH in very preterm newborns, with SGA or suspected FGR, and to stratify for severity of both FGR and IVH. The secondary aim was to identify risk factors for IVH in a large contemporary cohort. STUDY DESIGN: A population-based retrospective cohort study using data from the Australian and New Zealand Neonatal Network. Participants were babies born before 32 weeks' gestation (22-31 weeks + 6 days gestation) between 2014 and 2019 inclusive. The primary outcomes were IVH and severity of IVH. Small babies were classified as being SGA (SGA; birth weight <10th percentile), suspected FGR (birth weight <10th and >= 3rd birth weight percentile and abnormal antenatal ultrasound), or severe FGR (birth weight <3rd percentile). Multivariate regression was then performed, adjusting for potential maternal and fetal confounders to determine the association between FGR and IVH. RESULTS: 20,551 very preterm newborns were included in the study with a median gestational age (25th, 75th) of 29 (27, 30) weeks gestation and birth weight of 1201 (383.9) grams. The incidence of any IVH was 20.02% (n=4115) and increased with decreasing gestation at birth (10% of infants born at 31 weeks had IVH compared with 70% of infants born at 22 weeks). The rate of severe IVH (Grade 3 or 4) was 3.23%. In this cohort, 7.7% were SGA (n=1583) and 6.23% (n=1281) of babies had suspected early-onset FGR. The incidence of SGA was reduced in babies with IVH (6.0% vs 8.1%, respectively, aOR, 0.82; 95% CI 0.68-0.97). Similarly, suspected FGR was significantly lower in infants with IVH (any grade) compared to those without (2.5% vs 4.6%, respectively, adjusted odds ratio (aOR), 0.69; 95% CI 0.54-0.89). Further, there was a negative association between SGA (aOR, 0.80; 95% CI 0.67-0.95) and FGR (aOR 0.69; 95% CI 0.54-0.88) and the severity of IVH. Severe FGR (<3rd birth weight percentile) was not associated with either the presence (1.9% with IVH, vs 2.1% without IVH, aOR, 0.86; 95% CI 0.64-1.16) or severity of VH (aOR, 0.85; 95% CI 0.63-1.14). CONCLUSION: This large retrospective cohort study identified that in very preterm infants born with a median gestational age at birth of 29 weeks and who survive to the neonatal unit, the presence of SGA or suspected FGR is associated with a reduced rate of IVH, compared to infants without SGA/FGR. Future studies should directly assess whether placental insufficiency prevents the development of IVH, so that novel neuroprotective strategies for the very preterm infant can be implemented.

Early-onset fetal growth restriction (FGR) is associated with prolonged fetoplacental hypoxia and altered brain development, including deficits in hippocampal structure and function. Neuroprotective actions of lactoferrin have been described, mediated via anti-inflammatory and antioxidant properties. Here, we investigated whether the antenatal administration of lactoferrin (1) improves hippocampal structure, (2) promotes neuronal growth, and (3) mitigates neuroinflammation in the hippocampus of fetal sheep with FGR. Early-onset FGR was induced by performing single umbilical artery ligation surgery on ovine fetuses at ~89 days gestational age (dGA; term ~148 dGA), compared with appropriate for gestational age (AGA) controls. Lactoferrin supplementation to the ewe commenced at 95 dGA (oral, 36 g/day) and continued until 127 dGA (fetal group) or birth (newborn group). Experimental fetal groups included control appropriate for gestational age (AGA; n = 8), FGR (n = 5), control + lactoferrin (AGA + Lacto; n = 6), and FGR + lactoferrin (FGR + Lacto; n = 6). In the fetal group, results showed that neither FGR nor lactoferrin altered hippocampal structure at 127 dGA. Lactoferrin exposure significantly increased neuronal abundance but also altered neuronal morphology. Lactoferrin increased the neurotrophic factor, brain-derived neurotrophic factor (BDNF) in the hippocampus. Lactoferrin exerted region-specific anti-inflammatory effects, with reduced total microglial cell count and resting microglia count in the Cornu Ammonis (CA)3 region only. In the newborn cohort, we observed increased circulating haematocrit concentration in early life. These findings support that antenatal lactoferrin has an anti-inflammatory effect in the fetal brain and increases fetal brain neurotrophic factor BDNF. Still, prolonged exposure during pregnancy may yield mixed effects on fetal brain development and haematological balance.

The mechanisms that drive placental dysfunction in pregnancies complicated by hypoxia and fetal growth restriction remain poorly understood. Changes to mitochondrial respiration contribute to cellular dysfunction in conditions of hypoxia and have been implicated in the pathoaetiology of pregnancy complications, such as pre-eclampsia. We used bespoke isobaric hypoxic chambers and a combination of functional, molecular and imaging techniques to study cellular metabolism and mitochondrial dynamics in sheep undergoing hypoxic pregnancy. We show that hypoxic pregnancy in sheep triggers a shift in capacity away from beta-oxidation and complex I-mediated respiration, while maintaining total oxidative phosphorylation capacity. There are also complex-specific changes to electron transport chain composition and a switch in mitochondrial dynamics towards fission. Hypoxic placentas show increased activation of the non-canonical mitochondrial unfolded protein response pathway and enhanced insulin like growth factor 2 signalling. Combined, therefore, the data show that the hypoxic placenta undergoes significant metabolic and morphological adaptations to maintain cellular energy balance. Chronic hypoxia during pregnancy in sheep activated placental mitochondrial stress pathways, leading to alterations in mitochondrial respiration, mitochondrial energy metabolism and mitochondrial dynamics, as seen in the placenta of women with pre-eclampsia.