Cardiac Performance in the First Year of Age Among Preterm Infants Fed Maternal Breast Milk

Impact of maternal bariatric surgery on offspring perinatal cardiac function: A prospective study

OBJECTIVE

To assess perinatal cardiac function in offspring of women with previous bariatric surgery and examine its association with maternal glucose control.

DESIGN

Prospective study.

SETTING

Maternity unit, UK.

POPULATION

Fifty-four fetuses/neonates; 29 of post-bariatric surgery women and 25 of women without surgery.

METHODS

Prospective, longitudinal observational study of pregnant women with and without previous bariatric surgery, matched for early pregnancy body mass index. Cardiac function of all offspring was assessed by two-dimensional conventional, spectral tissue Doppler and speckle-tracking echocardiography at 35-37 weeks of gestation and at 5-7 weeks of age. Maternal glycated haemoglobin (HbA1c) was measured at 27-30 weeks of gestation. Maternal demographics and fetal/infant cardiac function indices were compared between the groups. Correlation coefficient (r) is reported.

MAIN OUTCOME MEASURES

Fetal/infant cardiac function indices.

RESULTS

Compared with no-bariatric neonates, offspring of post-bariatric women were smaller at birth (birthweight centiles: 64.96 ± 36.41 versus 40.17 ± 27.99; p = 0.007). There were no significant differences in fetal/infant cardiac function indices and perinatal cardiac changes, between groups. There was a positive correlation between maternal HbA1c and fetal left ventricular (LV) longitudinal strain (r = 0.33) and LV longitudinal strain rate (r = 0.29), suggesting an inverse relation between HbA1c and fetal LV systolic function, but this was mainly seen in offspring of women with no previous bariatric surgery (r = 0.56 and r = 0.50, respectively).

CONCLUSIONS

Maternal bariatric surgery does not appear to inadvertently affect the offspring cardiac performance. We found an inverse correlation between maternal HbA1c levels and fetal LV systolic function but this was mainly seen in the no-bariatric pregnancies.

Arterial hypertension in infants with congenital diaphragmatic hernia following surgical repair

Pulmonary hypertension (PH) and cardiac dysfunction are established comorbidities of congenital diaphragmatic hernia (CDH). However, there is very little data focusing on arterial hypertension in CDH. This study aims to investigate the incidence of arterial hypertension in neonates with CDH at hospital discharge. Archived clinical data of 167 CDH infants who received surgical repair of the diaphragmatic defect and survived for > 60 days were retrospectively analyzed. Blood pressure (BP) values were averaged for the last 7 days before discharge and compared to standard BP values for sex, age, and height provided by the AHA in 2004. BP values reaching or extending the 95th percentile were defined as arterial hypertension. The use of antihypertensive medication was analyzed at discharge and during hospitalization. Arterial hypertension at discharge was observed in 19 of 167 infants (11.3%) of which 12 (63%) were not receiving antihypertensive medication. Eighty patients (47.9%) received antihypertensive medication at any point during hospitalization and 28.9% of 152 survivors (n = 44) received antihypertensive medication at discharge, although in 45.5% (n = 20) of patients receiving antihypertensive medication, the indication for antihypertensive medication was myocardial hypertrophy or frequency control. BP was significantly higher in ECMO compared to non-ECMO patients, despite a similar incidence of arterial hypertension in both groups (13.8% vs. 10.1%, p = 0.473). Non-isolated CDH, formula feeding, and minimal creatinine in the first week of life were significantly associated with arterial hypertension on univariate analysis. Following multivariate analysis, only minimal creatinine remained independently associated with arterial hypertension.   Conclusion: This study demonstrates a moderately high incidence of arterial hypertension in CDH infants at discharge and an independent association of creatinine values with arterial hypertension. Physicians should be aware of this risk and include regular BP measurements and test of renal function in CDH care and follow-up. What is Known: • Due to decreasing mortality, morbidity is increasing in surviving CDH patients. • Pulmonary hypertension and cardiac dysfunction are well-known cardiovascular comorbidities of CDH. What is New: • There is a moderately high incidence of arterial hypertension in CDH infants at discharge even in a population with frequent treatment with antihypertensive medication. • A more complicated hospital course (ECMO, higher degree of PH, larger defect size) was associated with a higher risk for arterial hypertension.

Exclusive human milk feeding and prevalence of early adiposity rebound in ELBW infants: a retrospective cohort study

The purpose of the present study was to evaluate the prevalence of early adiposity rebound (EAR) and factors associated with its occurrence in a cohort of extremely low birth weight infants (ELBW). We conducted a retrospective longitudinal study including ELBW infants followed-up for up to 10 years after discharge. EAR was defined as occurring before 5 years of age. A multivariate binary logistic regression analysis was performed to evaluate maternal and perinatal variables independently associated with EAR. Out of 212 ELBW infants included in the analysis, 40.6% developed EAR and 21.5% showed it before 4 years of age. Only formula milk feeding at discharge was independently associated with a higher risk of EAR. The mean BMI of children with EAR was higher than that of children without EAR. Furthermore, the prevalence of overweight and obesity was higher in the EAR group than in the timely AR group.  Conclusions: ELBW infants in our cohort developed EAR in a relatively high percentage of cases. In this already at-risk population, EAR may represent a further risk factor for an adverse metabolic outcome. Monitoring preterm infants' growth within a long-term follow-up program and promoting and supporting human milk feeding is advisable. What is Known: • Preterm-born infants are at high risk for long-term adverse health outcomes, especially cardiovascular and metabolic. • The occurrence of early adiposity rebound (EAR) is associated with the risk of later obesity and metabolic syndrome. What is New: • The occurrence of EAR in ELBW infants may represent an additional risk factor for later adverse metabolic outcomes in an already vulnerable population. • Future preventive strategies should include a long-term follow-up and the promotion of exclusive breastfeeding.

Antisecretory factor in breastmilk is associated with reduced incidence of sepsis in preterm infants

BACKGROUND

Antisecretory Factor (AF) is a protein present in breastmilk that regulates inflammatory processes. We aimed to investigate the level of AF in mothers' own milk (MOM) in relation to sepsis and other neonatal morbidities in preterm infants.

METHODS

Samples of breastmilk and infant plasma were collected at 1, 4, and 12 weeks after birth from 38 mothers and their 49 infants born before 30 weeks gestation. AF-compleasome in MOM was determined by a sandwich enzyme-linked immunosorbent assay (ELISA) and inflammatory markers in infant plasma by a panel of 92 inflammatory proteins. Neonatal treatments and outcomes were recorded.

RESULTS

The level of AF in MOM week 1 was lower for infants with later sepsis compared to no sepsis (p = 0.005). Corrected for nutritional intake of MOM, higher levels of AF decreased the risk for sepsis, OR 0.24. AF in MOM week 1 was negatively correlated to inflammatory proteins in infant plasma week 4, markedly IL-8, which was also associated with infant sepsis. Overall, higher AF levels in MOM was associated with fewer major morbidities of prematurity.

CONCLUSION

Mother's milk containing high levels of antisecretory factor is associated with reduced risk for sepsis and inflammation in preterm infants.

IMPACT

High level of antisecretory factor (AF) in mothers' own milk is associated with less risk for later sepsis in preterm infants. Receiving mothers' milk with low AF levels during the first week after birth is correlated with more inflammatory proteins in infant's plasma 2-4 weeks later. Human breastmilk has anti-inflammatory properties, and antisecretory factor in mothers' own milk is a component of potential importance for infants born preterm. The findings suggest that food supplementation with AF to mothers of preterm infants to increase AF-levels in breastmilk may be a means to decrease the risk of inflammatory morbidities of prematurity.

Human colostrum in vitro protein digestion: peptidomics by liquid chromatography-Orbitrap-high-resolution MS and prospection for bioactive peptides via bioinformatics

Breast milk is known to contain bioactive peptides that are released during digestion, being a major source of bioactive peptides to the new-born, some of which act against invading pathogens. However, the formation of bioactive peptides during digestion of human colostrum remains largely uninvestigated. This study aimed to investigate the formation of peptides during simulated digestion of human colostrum from adult women and to prospect antimicrobial peptides. For this purpose, we used high-resolution MS to monitor the release of peptides during in vitro digestion. Bioinformatics was used for the prospection of antimicrobial activity of peptides. During simulated digestion (oral, gastric and duodenal phases), 2318 peptide sequences derived from 112 precursor proteins were identified. At the end of simulated digestion, casein-derived peptide sequences were the most frequently observed. Among precursors, some proteins were seen for the first time in this study. The resulting peptides were rich in proline, glutamine, valine and leucine residues, providing characteristic traits of antimicrobial peptides. From bioinformatics analysis, seven peptides showed potentially high antimicrobial activity towards bacteria, viruses and fungi, from which the latter was the most prominent predicted activity. Antimicrobial peptides released during digestion may provide a defence platform with controlled release for the new-born.

Risk Factors for Adverse Outcomes in Term Infants with CHD and Definitive Necrotising Enterocolitis

OBJECTIVES

To define the incidence of definitive necrotising enterocolitis in term infants with CHD and identify risk factors for morbidity/mortality.

METHODS

We performed a 20-year (2000-2020) single-institution retrospective cohort study of term infants with CHD admitted to the Boston Children's Hospital cardiac ICU with necrotising enterocolitis (Bell's stage ≥ II). The primary outcome was a composite of in-hospital mortality and post-necrotising enterocolitis morbidity (need for extracorporeal membrane oxygenation, multisystem organ failure based on the paediatric sequential organ failure assessment score, and/or need for acute gastrointestinal intervention). Predictors included patient characteristics, cardiac diagnosis/interventions, feeding regimen, and severity measures.

RESULTS

Of 3933 term infants with CHD, 2.1% (n = 82) developed necrotising enterocolitis, with 67% diagnosed post-cardiac intervention. Thirty (37%) met criteria for the primary outcome. In-hospital mortality occurred in 14 infants (17%), of which nine (11%) deaths were attributable to necrotising enterocolitis. Independent predictors of the primary outcome included moderate to severe systolic ventricular dysfunction (odds ratio 13.4,confidence intervals 1.13-159) and central line infections pre-necrotising enterocolitis diagnosis (odds ratio 17.7, confidence intervals 3.21-97.0) and mechanical ventilation post-necrotising enterocolitis diagnosis (odds ratio 13.5, confidence intervals 3.34-54.4). Single ventricle, ductal dependency, and feeding related factors were not independently associated with the primary outcome.

CONCLUSIONS

The incidence of necrotising enterocolitis was 2.1% in term infants with CHD. Adverse outcomes occurred in greater than 30% of patients. Presence of systolic dysfunction and central line infections prior to diagnosis and need for mechanical ventilation after diagnosis of necrotising enterocolitis can inform risk triage and prognostic counseling for families.

Dose-dependent impact of human milk feeding on tidal breathing flow-volume loop parameters across the first 2 years of life in extremely low-birth-weight infants: a cohort study

The purpose of this study is to test the hypothesis that higher consumption of human milk (HM) in preterm infants with birth weight (BW) <1000 g is associated with improved lung function in a dose-dependent manner over the first 2 years of corrected age (CA). This retrospective study at an academic medical center included infants with BW <1000g. They had lung function assessment by the tidal breathing flow-volume loop (TBFVL) follow-up visits at 0-3-, 3-6-, 6-12-, 12-18-, and 18-24-month CA. One hundred eighty infants were included in the study with a mean (SD) gestational age 26.5 (1.90) weeks and BW 772.4 (147.0) g, 50% were female, and 60% developed BPD. 62.8% of infants received HM during the NICU stay. According to a general linear model (including GA, being small for GA (SGA), sex, human milk percentage, sepsis, and BPD), on average, each week of GA resulted in a higher tPTEF/tE of 1.24 (p = 0.039) and being SGA in a lower tPTEF/tE of 5.75 (p = 0.013) at 0-3-month CA. A higher percentage of human milk out of the total enteral intake was associated with better tPTEF/tE z-scores at 0-3 months (p = 0.004) and 18-24 months of CA (p = 0.041). BPD diagnosis was associated with a relevantly worse tPTEF/tE z-score at 6-12 months of CA (p = 0.003).

CONCLUSION

Preterm infants with higher consumption of HM had significantly less airway obstruction across the first 2 years, suggesting that human milk may contribute in a dose-dependent manner to improve lung function in early childhood in former preterm infants born ELBW.

WHAT IS KNOWN

• Human milk feeding reduces the risk of prematurity-related morbidities, including necrotizing enterocolitis, sepsis, lower respiratory tract infections, and BPD. Both exclusive and partial human milk feeding appear to be associated with a lower risk of BPD in preterm infants.

WHAT IS NEW

• This cohort study of 180 preterm infants with birth weight < 1000 g found that exposure to human milk during hospitalization improves airway obstruction markers tPTEF/tE z-score over the first 2 years of corrected age in a dose-dependent manner.

P-Wave Axis of Schoolchildren Who Were Once Breastfed

BACKGROUND

It has been known for decades that breastfeeding leads to a lower risk of asthma, respiratory infections, or metabolic syndrome at school age. In addition, evidence is now accumulating on the influence of breast milk on the shape, volume, or function of the heart and lungs. Within this field of research into the effects of breast milk on the structure of the heart and lungs, we have set out to analyze the differential electrocardiographic characteristics of schoolchildren who were once breastfed.

METHOD

This was an observational cross-sectional study, including 138 children aged 6 or 12 consecutively presenting to a well-child clinic between May and December 2022.

INCLUSION CRITERIA

The ability to perform reproducible ECG records, the feasibility of weighing and measuring patient, and breastfeeding data collected from birth were used as the inclusion criteria.

RESULTS

Using the 40° cut-off value for the mean P-wave axis among schoolchildren, 76% of never-breastfed children in our sample have a P-wave axis in a more vertical position than the mean as compared to 58% of ever-breastfed children (OR: 2.25; 95% CI: 3.13-1.36); there was no other significant difference between infant feeding groups in somatometric characteristics or ECG parameters.

CONCLUSION

We found a significant difference of the mean values of the P-wave axis between never- and ever-breastfed children. Although this report should be approached cautiously, these findings add to the renewed interest in discerning developmental interventions to improve cardiovascular health.

Exploring Human Milk, Nutrition, Growth, and Breastfeeding Rates at Discharge(HUMMINGBIRD Study): a protocol for a pilot randomised controlled trial

INTRODUCTION

Mother's own breast milk (MOM) is the optimal nutrition for preterm infants as it reduces the incidence of key neonatal morbidities and improves long-term outcomes. However, MOM shortfall is common and either preterm formula or pasteurised donor human milk (DHM) may be used, although practice varies widely. Limited data suggest that the use of DHM may impact maternal beliefs and behaviours and therefore breastfeeding rates. The aim of this pilot study is to determine if longer duration of DHM exposure increases breastfeeding rates, and if a randomised controlled trial (RCT) design is feasible.

METHODS AND ANALYSIS

The Human Milk, Nutrition, Growth, and Breastfeeding Rates at Discharge (HUMMINGBIRD) Study is a feasibility and pilot, non-blinded RCT with a contemporaneous qualitative evaluation. Babies born less than 33 weeks' gestation or with birth weight <1500 g whose mothers intend to provide MOM are randomly assigned to either control (DHM used to make up shortfall until full feeds and preterm formula thereafter) or intervention (DHM used for shortfall until 36 weeks' corrected age or discharge if sooner). The primary outcome is breast feeding at discharge. Secondary outcomes include growth, neonatal morbidities, length of stay, breastfeeding self-efficacy and postnatal depression using validated questionnaires. Qualitative interviews using a topic guide will explore perceptions around use of DHM and analysed using thematic analysis.

ETHICS APPROVAL AND DISSEMINATION

Nottingham 2 Research Ethics Committee granted approval (IRAS Project ID 281071) and recruitment commenced on 7 June 2021. Results will be disseminated in peer-reviewed journals.

TRIAL REGISTRATION NUMBER

ISRCTN57339063.

The role of human milk feeds on inotrope use in newborn infants with sepsis

Background

Regarding neonatal hypotension, there is no certainty as to whether inotrope properties are beneficial or whether they may be harmful. However, given that the antioxidant content of human milk plays a compensatory role in neonatal sepsis and that human milk feeding has direct effects in modulating the cardiovascular function of sick neonates, this research hypothesized that human milk feeds might predict lower requirements of vasopressors in the management of neonatal septic shock.

Method

Between January 2002 and December 2017, all late preterm and full-term infants attending a neonatal intensive care unit, with clinical and laboratory findings of bacterial or viral sepsis, were identified in a retrospective study. During their first month of life, data on feeding type and early clinical characteristics were collected. A multivariable logistic regression model was constructed to determine the impact of human milk on the use of vasoactive drugs in septic newborns.

Results

322 newborn infants were eligible to participate in this analysis. Exclusively formula-fed infants were more likely to be delivered via C-section, to have a lower birth weight and a lower 1-minute Apgar score than their counterparts. Human milk-fed newborns had 77% (adjusted OR = 0.231; 95% CI: 0.07-0.75) lower odds of receiving vasopressors than exclusively formula-fed newborns.

Conclusion

We report that any human milk feeding is associated with a decrease in the need for vasoactive medications in sepsis-affected newborns. This observation encourages us to undertake further research to determine whether human milk feeds mitigate the use of vasopressors in neonates with sepsis.

Differing Impact of Preterm Birth on the Right and Left Atria in Adulthood

Background Preterm birth affects 10% of live births and is associated with an altered left ventricular and right ventricular phenotype and increased cardiovascular disease risk in young adulthood. Because left atrial (LA) and right atrial (RA) volume and function are known independent predictors of cardiovascular outcomes, we investigated whether these were altered in preterm-born young adults. Methods and Results Preterm-born (n=200) and term-born (n=266) adults aged 18 to 39 years underwent cardiovascular magnetic resonance imaging. LA and RA maximal and minimal volumes (absolute, indexed to body surface area, and as a ratio to ventricular volumes) were obtained to study atrial morphology, while LA and RA stroke volume, strain, and strain rate were used to assess atrial function. Secondary analyses consisted of between-group comparisons based on degree of prematurity. Absolute RA volumes and RA volumes indexed to right ventricular volumes were significantly smaller in preterm-born compared with term-born adults. In addition, RA reservoir and booster strain were higher in preterm-born adults, possibly indicating functional compensation for the smaller RA volumes. LA volumes indexed to left ventricular volumes were significantly greater in preterm-born adults as compared with term-born adults, although absolute LA volumes were similar between groups. LA and RA changes were observed across gestational ages in the preterm group but were greatest in those born very-to-extremely preterm. Conclusions Preterm-born adults show changes in LA and RA structure and function, which may indicate subclinical cardiovascular disease. Further research into underlying mechanisms, opportunities for interventions, and their prognostic value is warranted.

Evolution of Preterm Infant Nutrition from Breastfeeding to an Exclusive Human Milk Diet: A Review

The benefits of feeding human milk to human infants are well-established. Preterm infants, particularly those born with very low birthweight (VLBW; <1,500 g), are a uniquely vulnerable population at risk for serious, life-threatening complications as well as disruptions in normal growth and development that can affect their lives into adulthood. Feeding VLBW preterm infants an exclusive human milk diet (EHMD) from birth that consists of the mother's own milk or donor human milk plus a nutritional fortifier made exclusively from human milk has been associated with a reduction in morbidity and mortality and improved early growth and developmental metrics. Preliminary evidence suggests that the health benefits of adopting an EHMD (or avoiding cow milk products) early in life may last into adulthood. This review briefly summarizes the history of breastfeeding and describes the available evidence on the benefits of an EHMD among VLBW preterm infants as well as the importance of high-quality manufacturing standards for producing safe and effective human milk-based products.

Rethinking Congenital Heart Disease in Preterm Neonates

Congenital heart disease (CHD) and prematurity are the leading causes of infant mortality in the United States. Importantly, the combination of prematurity and CHD results in a further increased risk of mortality and significant morbidity. The key factors in these adverse outcomes are not well understood, but likely include maternal-fetal environment, perinatal and neonatal elements, and challenging postnatal care. Preterm neonates with CHD are born with "double jeopardy": not only do they experience challenges related to immaturity of the lungs, brain, and other organs, but they also must undergo treatment for cardiac disease. The role of the neonatologist caring for preterm infants with CHD has changed with the evolution of the field of pediatric cardiac critical care. Increasingly, neonatologists invested in the cardiovascular care of the newborn with CHD engage at multiple stages in their course, including fetal consultation, delivery room management, preoperative care, and postoperative treatment. A more comprehensive understanding of prematurity and CHD may inform clinical practice and ultimately improve outcomes in preterm infants with CHD. In this review, we discuss the current evidence surrounding neonatal and cardiac outcomes in preterm infants with CHD; examine the prenatal, perinatal, and postnatal factors recognized to influence these outcomes; identify knowledge gaps; consider research and clinical opportunities; and highlight the ways in which a neonatologist can contribute to the care of preterm infants with CHD.

Echocardiographic Assessment of Pulmonary Hypertension in Neonates with Congenital Diaphragmatic Hernia Using Pulmonary Artery Flow Characteristics

Background: Assessment of pulmonary hypertension (PH) is essential in neonates with congenital diaphragmatic hernia (CDH). Echocardiography is widely established to quantify PH severity, but currently used parameters have inherent limitations. The aim of our study was to investigate the prognostic utility of the index of the pulmonary artery acceleration time to the right ventricular ejection time (PAAT:ET) in CDH neonates assessed using echocardiography. Methods: PAAT:ET values were prospectively measured in CDH neonates on admission, on day of life (DOL) 2 and DOL 5−7. Optimal cut-off values to predict mortality and need for ECMO were calculated and PAAT:ET values were compared between non-ECMO survivors, ECMO-survivors, and ECMO-non-survivors. Results: 87 CDH neonates were enrolled and 39 patients required ECMO therapy. At baseline, PAAT:ET values were significantly lower in ECMO patients compared to non-ECMO patients (p < 0.001). ECMO survivors and ECMO non-survivors had similar values at baseline (p = 0.967) and DOL 2 (p = 0.124) but significantly higher values at DOL 5−7 (p = 0.003). Optimal PAAT:ET cut-off for predicting ECMO was 0.290 at baseline and 0.310 for predicting non-survival in patients on ECMO at DOL 5−7. Conclusion: PAAT:ET is a feasible parameter for early risk assessment in CDH neonates.

Acute and chronic cardiac adaptations in adults born preterm

New Findings

What is the topic of this review?

Studies using cardiovascular magnetic resonance imaging and echocardiography to investigate cardiac alterations at rest and during exercise‐induced physiological stress in adults born preterm.

What advances does it highlight?

People born preterm have a greater long‐term cardiovascular risk, which may be explained in part by their cardiac structural and functional alterations. They have potentially adverse alterations in left and right ventricular structure and function that worsens with blood pressure elevation; an impaired myocardial functional reserve; and an increase in diffuse myocardial fibrosis that may drive their lower diastolic function.

Abstract

Preterm birth accounts for more than 10% of births worldwide and associates with a long‐term increase in cardiovascular disease risk. The period around preterm birth is a rapid and critical phase of cardiovascular development, which might explain why changes in multiple components of the cardiovascular system have been observed in individuals born preterm. These alterations include reduced microvascular density, increased macrovascular stiffness, and higher systolic and diastolic blood pressure. Cardiac alterations have been observed in people born preterm as early as neonatal life and infancy, with potentially adverse changes in both left and right ventricular structure and function extending into adulthood. Indeed, studies using cardiovascular magnetic resonance imaging and echocardiography have demonstrated that preterm‐born individuals have structural cardiac changes and functional impairments. Furthermore, myocardial tissue characterization by cardiovascular magnetic resonance imaging has demonstrated an increase in left ventricular diffuse myocardial fibrosis in young adults born preterm, and under acute physiological stress, their myocardial functional reserve assessed by echocardiography is reduced. The preterm heart is also more susceptible to chronic systolic blood pressure elevation, with a significantly greater increase in left ventricular mass as systolic blood pressure rises observed in preterm‐born compared to term‐born young adults. Given these known, potentially adverse acute and chronic cardiac adaptations in the preterm‐born population, primary prevention strategies are needed to reduce long‐term cardiovascular disease risk in this subgroup of the population.

Understanding the Preterm Human Heart: What do We Know So Far?

Globally, preterm birth affects more than one in every 10 live births. Although the short‐term cardiopulmonary complications of prematurity are well known, long‐term health effects are only now becoming apparent. Indeed, preterm birth has been associated with elevated cardiovascular morbidity and mortality in adulthood. Experimental animal models and observational human studies point toward changes in heart morphology and function from birth to adulthood in people born preterm that may contribute to known long‐term risks. Moreover, recent data support the notion of a heterogeneous cardiac phenotype of prematurity, which is likely driven by various maternal, early, and late life factors. This review aims to describe the early fetal‐to‐neonatal transition in preterm birth, the different structural and functional changes of the preterm human heart across developmental stages, as well as potential factors contributing to the cardiac phenotype of prematurity.