Influence of intrauterine growth restriction on airway development in fetal and postnatal sheep

In utero exposure to experimental maternal asthma alters fetal airway development in sheep

The mechanisms linking maternal asthma (MA) exposure in utero and subsequent risk of asthma in childhood are not fully understood. Pathological airway remodelling, including reticular basement membrane thickening, has been reported in infants and children who go on to develop asthma later in childhood. This suggests altered airway development before birth as a mechanism underlying increased risk of asthma in children exposed in utero to MA. We hypothesised that in utero MA exposure would reduce airway diameter and increase airway-associated smooth muscle area and reticular basement membrane thickness in neonatal offspring. Experimental MA was induced by maternal sensitisation followed by airway challenges with house dust mite before and during pregnancy. Lambs from control (n = 16) or MA (n = 26) ewes were delivered at ∼140 days gestation (term = 150 days), ventilated for 45 min, then humanely killed. Left lungs were inflation-fixed, and cross-sections of generation 2-5 airways were collected. Airway sections were stained with Haematoxylin and Eosin, Masson's Trichrome and Gordon and Sweet's histological stains for morphological analysis. Lamb body and lung weights were similar between groups (P > 0.5 and P > 0.7, respectively). Lambs that were exposed to MA had narrower airway diameters (P = 0.019) and thinner reticular basement membrane (P = 0.016) but similar airway-associated smooth muscle area (P = 0.152) compared with unexposed control lambs. Our results demonstrate a potential mechanism for increased risk of asthma in children of mothers with asthma, independent of genetic risk or behavioural changes during pregnancy.

Prenatal Origins of Obstructive Airway Disease: Starting on the Wrong Trajectory?

From the results of well-performed population health studies, we now have excellent data demonstrating that deficits in adult lung function may be present early in life, possibly as a result of developmental disorders, incurring a lifelong risk of obstructive airway diseases such as asthma and chronic obstructive pulmonary disease. Suboptimal fetal development results in intrauterine growth restriction and low birth weight at term (an outcome distinct from preterm complications), which are associated with subsequent obstructive disease. Numerous prenatal exposures and disorders compromise fetal development and these are summarized herein. Various physiological, structural, and mechanical abnormalities may result from prenatal disruption, including changes to airway smooth muscle structure-function, goblet cell biology, airway stiffness, geometry of the bronchial tree, lung parenchymal structure and mechanics, respiratory skeletal muscle contraction, and pulmonary inflammation. The literature therefore supports the need for early life intervention to prevent or correct growth defects, which may include simple nutritional or antioxidant therapy. © 2024 American Physiological Society. Compr Physiol 14:5729-5762, 2024.

Fetal thoracic circumference in mid-pregnancy and infant lung function

BACKGROUND AND AIM

Impaired lung function in early infancy is associated with later wheeze and asthma, while fetal thoracic circumference (TC) predicts severity of neonatal lung hypoplasia. Exploring fetal origins of lung function in infancy, we aimed to determine if fetal TC in mid-pregnancy was associated with infant lung function.

METHODS

From the prospective Scandinavian general population-based PreventADALL mother-child birth cohort, all 851 3-month-old infants with tidal flow-volume measurements in the awake state and ultrasound fetal size measures at 18 (min-max 16-22) weeks gestational age were included. Associations between fetal TC and time to peak tidal expiratory flow to expiratory time (t_PTEF /t_E ) were analyzed in linear regression models. To account for gestational age variation, we adjusted TC for simultaneously measured general fetal size, by head circumference (TC/HC), abdominal circumference (TC/AC), and femur length (TC/FL). Multivariable models were adjusted for maternal age, maternal asthma, pre-pregnancy body mass index, parity, nicotine exposure in utero, and infant sex.

RESULTS

The infants (47.8% girls) were born at mean (SD) gestational age of 40.2 (1.30) weeks. The mean (SD) t_PTEF /t_E  was 0.39 (0.08). The mean (SD) TC/HC was 0.75 (0.04), TC/AC 0.87 (0.04), and TC/FL 4.17 (0.26), respectively. Neither TC/HC nor TC/AC were associated with infant t_PTEF /t_E while a week inverse association was observed between TC/FL and t_PTEF /t_E  ( β ^ $\hat{\beta }$  = -0.03, 95% confidence interval [-0.05, -0.007], p = 0.01).

CONCLUSION

Mid-pregnancy fetal TC adjusted for fetal head or abdominal size was not associated with t_PTEF /t_E in healthy, awake 3-month-old infants, while a weak association was observed adjusting for fetal femur length.

Poor early childhood growth is associated with impaired lung function: Evidence from a Ghanaian pregnancy cohort

OBJECTIVES

Nearly 40% of African children under 5 are stunted. We leveraged the Ghana randomized air pollution and health study (GRAPHS) cohort to examine whether poorer growth was associated with worse childhood lung function.

STUDY DESIGN

GRAPHS measured infant weight and length at birth and 3, 6, 9,12 months, and 4 years of age. At age 4 years, n = 567 children performed impulse oscillometry. We employed multivariable linear regression to estimate associations between birth and age 4 years anthropometry and lung function. Next, we employed latent class growth analysis (LCGA) to generate growth trajectories through age 4 years. We employed linear regression to examine associations between growth trajectory assignment and lung function.

RESULTS

Birth weight and age 4 weight-for-age and height-for-age z-scores were inversely associated with airway resistance (e.g., R5 , or total airway resistance: birth weight β = -0.90 cmH2O/L/s, 95% confidence interval [CI]: -1.64, -0.16 per 1 kg increase; and R20 , or large airway resistance: age 4 height-for-age β = -0.40 cmH2O/L/s, 95% CI: -0.57, -0.22 per 1 unit z-score increase). Impaired growth trajectories identified through LCGA were associated with higher airway resistance, even after adjusting for age 4 body mass index. For example, children assigned to a persistently stunted trajectory had higher R5 (β = 2.71 cmH2O/L/s, 95% CI: 1.07, 4.34) and R20 (β = 1.43 cmH2O/L/s, 95% CI: 0.51, 2.36) as compared to normal.

CONCLUSION

Children with poorer anthropometrics through to age 4 years had higher airway resistance in early childhood. These findings have implications for lifelong lung health, including pneumonia risk in childhood and reduced maximally attainable lung function in adulthood.

Pediatric respiratory hospitalizations in small for gestational age neonates born at term

OBJECTIVE

This study investigates the risk for long-term respiratory hospitalizations of offspring born small for gestational age (SGA) at term.

STUDY DESIGN

A retrospective population-based cohort analysis was performed to examine the risk of long-term respiratory hospitalizations between SGA compared to appropriate for gestational age (AGA) newborns. The analysis included all term singleton deliveries occurring between 1991 and 2014 at a single tertiary medical center. Fetuses with congenital malformations, multiple gestation, cases of perinatal mortality and large for gestational age (LGA) were excluded. A Kaplan-Meier survival curve was used to compare cumulative morbidity incidence up to the age of 18 years, and a Cox hazards regression model was used to control for confounders.

RESULTS

During the study period 216,671 deliveries met the inclusion criteria; of them 4.8% (n = 10,450) were diagnosed as SGA neonates. During the follow-up period, the rate of hospitalization due to respiratory morbidity was significantly higher in the SGA group as compared to the AGA group (5.2% vs. 4.7%, OR = 1.13, 95% confidence interval [CI] = 1.03-1.24, p = 0.011). The Kaplan-Meier survival curve demonstrated a significantly higher cumulative incidence of respiratory morbidity in the SGA group (log-rank p = 0.026). In the Cox hazards regression model, controlled for relevant clinical confounders, SGA was found to be an independent risk factor for long-term pediatric respiratory morbidity (adjusted hazard ratio [HR] = 1.1, 95% CI = 1.001-1.19, p = 0.049).

CONCLUSION

Being delivered SGA at term is an independent long-term risk factor for pediatric respiratory hospitalization.

Fetal Growth Restriction and Asthma: Is the Damage Done?

Trajectories of airway remodeling and functional impairment in asthma are consistent with the notion that airway pathology precedes or coincides with the onset of asthma symptoms and may be present at birth. An association between intrauterine growth restriction (IUGR) and asthma development has also been established, and there is value in understanding the underlying mechanism. This review considers airway pathophysiology as a consequence of IUGR that increases susceptibility to asthma.

Intrauterine growth restriction predisposes to airway inflammation without disruption of epithelial integrity in postnatal male mice

Evidence from animal models demonstrate that intrauterine growth restriction (IUGR) alters airway structure and function which may affect susceptibility to disease. Airway inflammation and dysregulated epithelial barrier properties are features of asthma which have not been examined in the context of IUGR. This study used a maternal hypoxia-induced IUGR mouse model to assess lung-specific and systemic inflammation and airway epithelial tight junctions (TJs) protein expression. Pregnant BALB/c mice were housed under hypoxic conditions (10.5% O2) from gestational day (GD) 11 to 17.5 (IUGR group; term, GD 21). Following hypoxic exposure, mice were returned to a normoxic environment (21% O2). A Control group was housed under normoxic conditions throughout pregnancy. Offspring weights were recorded at 2 and 8 weeks of age and euthanized for bronchoalveolar lavage (BAL) and peritoneal cavity fluid collection for inflammatory cells counts. From a separate group of mice, right lungs were collected for Western blotting of TJs proteins. IUGR offspring had greater inflammatory cells in the BAL fluid but not in peritoneal fluid compared with Controls. At 8 weeks of age, interleukin (IL)-2, IL-13, and eotaxin concentrations were higher in male IUGR compared with male Control offspring but not in females. IUGR had no effect on TJs protein expression. Maternal hypoxia-induced IUGR increases inflammatory cells in the BAL fluid of IUGR offspring with no difference in TJs protein expression. Increased cytokine release, specific to the lungs of IUGR male offspring, indicates that both IUGR and sex can influence susceptibility to airway disease.

Neonatal outcome of small for gestational age infants born at 26-33 weeks' gestation in Chinese neonatal intensive care units

BACKGROUND

Rate and outcomes of small for gestational age (SGA) infants admitted to Chinese neonatal intensive care units (NICU) has been poorly demonstrated. We aimed to describe the rate and outcomes of SGA preterm infants in Chinese NICU, and to evaluate the association of SGA status with neonatal outcomes in different gestational age (GA) and birth weight percentile groups.

METHODS

This cohort study included all infants born at 26-33 weeks' gestation and admitted to 25 tertiary Chinese NICUs from April 2015 to May 2018. SGA was defined as a birthweight <10th percentile for GA based on the Chinese neonatal birth weight curve.

RESULTS

A total of 24,596 infants were included, and 1,867 (7.6%) infants were SGA. SGA infants had significantly higher rates of death or any major morbidity (29.8% vs. 20.5%), mortality (7.0% vs. 4.1%), bronchopulmonary dysplasia (BPD, 17.6% vs. 9.8%), necrotizing enterocolitis (NEC, 4.8% vs. 3.2%) and sepsis (7.3% vs. 4.8%) than non-SGA infants. SGA status was independently associated with increased risk of death or any major morbidity [adjusted odds ratio: 2.37 (2.08-2.71)] as well as increased risks of death, BPD, ROP, death or BPD, death or ROP, NEC and sepsis. The increased risks of adverse outcomes for SGA infants existed across GA groups. The risks of adverse outcomes were highest among infants with a birthweight <3rd percentile.

CONCLUSIONS

SGA contributes significantly to adverse neonatal outcomes. Specific attentions are warranted when caring for SGA preterm infants.

Adverse effects of small for gestational age differ by gestational week among very preterm infants

OBJECTIVE

To characterise the excess risk for death, grade 3-4 intraventricular haemorrhage (IVH), bronchopulmonary dysplasia (BPD) and stage 3-5 retinopathy of prematurity independently associated with birth small for gestational age (SGA) among very preterm infants, stratified by completed weeks of gestation.

METHODS

Retrospective cohort study using the Optum Neonatal Database. Study infants were born <32 weeks gestation without severe congenital anomalies. SGA was defined as a birth weight <10th percentile. The excess outcome risk independently associated with SGA birth among SGA babies was assessed using adjusted risk differences (aRDs).

RESULTS

Of 6708 infants sampled from 717 US hospitals, 743 (11.1%) were SGA. SGA compared with non-SGA infants experienced higher unadjusted rates of each study outcome except grade 3-4 IVH among survivors. The excess risk independently associated with SGA birth varied by outcome and gestational age. The highest aRD for death (0.27; 95% CI 0.13 to 0.40) occurred among infants born at 24 weeks gestation and declined as gestational age increased. In contrast, the peak aRDs for BPD among survivors (0.32; 95% CI 0.20 to 0.44) and the composites of death or BPD (0.35; 95% CI 0.24 to 0.46) and death or major morbidity (0.35; 95% CI 0.24 to 0.45) occurred at 27 weeks gestation. The risk-adjusted probability of dying or developing one or more of the evaluated morbidities among SGA infants was similar to that of non-SGA infants born approximately 2-3 weeks less mature.

CONCLUSION

The excess risk for neonatal morbidity and mortality associated with being born SGA varies by adverse outcome and gestational age.

Nutrition and Lung Growth

Experimental evidence from animal models and epidemiology studies has demonstrated that nutrition affects lung development and may have a lifelong impact on respiratory health. Chronic restriction of nutrients and/or oxygen during pregnancy causes structural changes in the airways and parenchyma that may result in abnormal lung function, which is tracked throughout life. Inadequate nutritional management in very premature infants hampers lung growth and may be a contributing factor in the pathogenesis of bronchopulmonary dysplasia. Recent evidence seems to indicate that infant and childhood malnutrition does not determine lung function impairment even in the presence of reduced lung size due to delayed body growth. This review will focus on the effects of malnutrition occurring at critical time periods such as pregnancy, early life, and childhood, on lung growth and long-term lung function.

Increased heterogeneity of airway calibre in adult rats after hypoxia-induced intrauterine growth restriction

BACKGROUND AND OBJECTIVE

Intrauterine growth restriction (IUGR) is associated with asthma development. We hypothesized that IUGR disrupts airway development leading to postnatal structural abnormalities of the airway that predispose to disease. This study therefore examined structural changes to the airway and lung in a rat model of maternal hypoxia-induced IUGR.

METHODS

Pregnant rats were housed under hypoxic conditions (11.5% O₂ ) from gestational days (GDs) 13 to 20 (pseudoglandular-canalicular stages, i.e. period of airway development) and then returned to normoxic conditions (21% O₂ ). A control group of pregnant rats was housed under normoxic conditions throughout pregnancy. Weights of male offspring were recorded at birth and 7 weeks of age (adulthood), at which point lungs were fixed for morphometry and stereology (n = 6/group), or bronchoalveolar lavage fluid (BALF) was collected for cell counts (n = 6/group).

RESULTS

IUGR offspring were lighter at birth compared with control, but not at 7 weeks. While there was no difference in mean airway dimensions or lung volume, there was greater anatomical variation in airway lumen area in the IUGR group. A mathematical model of the human lung was used to show that greater heterogeneity in lumen area in IUGR-affected individuals increases bronchoconstriction during simulated bronchial challenge. More macrophages were identified in the BALF of IUGR offspring.

CONCLUSION

The rat model demonstrates that IUGR leads to a more heterogeneous distribution of airway lumen calibre in adulthood with potential implications for bronchoconstriction in human subjects. Together with increased lung macrophages, these findings support a phenotypic shift after IUGR that may impact disease susceptibility.

Foetal and infant growth patterns, airway resistance and school-age asthma

BACKGROUND AND OBJECTIVE

Preterm birth, low birth weight and rapid infant weight gain are associated with increased risks of asthma symptoms in childhood. The underlying mechanism may include persistently higher airway resistance (Rint). The aim of our study was to examine the associations of longitudinally measured foetal and infant growth characteristics with Rint and asthma outcomes in school-age children.

METHODS

This study was embedded in a population-based prospective cohort study in Rotterdam, The Netherlands. Foetal growth was estimated by ultrasound in the second and third trimesters. Infant growth was measured at birth, 3, 6 and 12 months. At age 6 years, Rint was measured, and information about wheezing and asthma was obtained by questionnaires. The number of subjects per analysis differed per available outcome (3954-5066 subjects).

RESULTS

Longitudinal growth analyses showed that school-age children with increased Rint had lower foetal length growth and weight gain, and lower infant length growth. Children with persistent wheezing until age 6 years and physician-diagnosed asthma had a higher Rint compared with children who never wheezed or without asthma (difference z-scores Rint: 0.58 (0.19, 0.97) and 0.55 (0.15, 0.95), respectively).

CONCLUSION

Rint in school-age children is influenced by foetal growth restriction and is associated with asthma outcomes. See article, page 574.

Impact of intrauterine growth restriction on preterm lung disease

AIM

Intrauterine growth restriction (IUGR) is an important cause for prematurity and adversely influences prematurity-related morbidities. This study evaluates the impact of IUGR on respiratory outcomes in infants <32 weeks with IUGR and birthweight <10th centile (SGA) compared to matched appropriate for gestation (AGA) controls.

METHODS

The primary outcomes of this retrospective study are short-term pulmonary outcomes of chronic lung disease (CLD), CLD or death, and need for home oxygen at discharge. Subgroup analysis by gestation-based stratification (<28 and ≥28 <32 weeks) was decided a priori.

RESULTS

Total of 153 IUGR and 306 non-IUGR infants were enrolled. The rate of CLD (45% vs. 17%, p = 0.0001), death (16% vs. 4.6%, p = 0.0001), CLD or death (46% vs. 21.5%, p = 0.0001), home oxygen rates (13.7% vs. 6.5%, p = 0.01) and duration of respiratory support was significantly higher in the IUGR group. IUGR emerged as the strongest predictor of CLD (adjusted OR, 95%CI: (8.4 [2, 35]) and CLD or death (12.7 [3, 54]) across all gestation.

CONCLUSION

IUGR is a major risk factor for adverse short-term pulmonary outcomes as reflected by higher rates of CLD, CLD or death, and oxygen dependency at discharge in preterm infants.

Influence of childhood growth on asthma and lung function in adolescence

Background

Low birth weight and rapid infant growth in early infancy are associated with increased risk of childhood asthma, but little is known about the role of postinfancy growth in asthmatic children.

Objectives

We sought to examine the associations of children's growth patterns with asthma, bronchial responsiveness, and lung function until adolescence.

Methods

Individual growth trajectories from birth until 10 years of age were estimated by using linear spline multilevel models for 9723 children participating in a population-based prospective cohort study. Current asthma at 8, 14, and 17 years of age was based on questionnaires. Lung function and bronchial responsiveness or reversibility were measured during clinic visits at 8 and 15 years of age.

Results

Rapid weight growth between 0 and 3 months of age was most consistently associated with increased risks of current asthma at the ages of 8 and 17 years, bronchial responsiveness at age 8 years, and bronchial reversibility at age 15 years. Rapid weight growth was associated with lung function values, with the strongest associations for weight gain between 3 and 7 years of age and higher forced vital capacity (FVC) and FEV₁ values at age 15 years (0.12 [95% CI, 0.08 to 0.17] and 0.11 [95% CI, 0.07 to 0.15], z score per SD, respectively) and weight growth between 0 and 3 months of age and lower FEV₁/FVC ratios at age 8 and 15 years (−0.13 [95% CI, −0.16 to −0.10] and −0.04 [95% CI, −0.07 to −0.01], z score per SD, respectively). Rapid length growth was associated with lower FVC and FVC₁ values at age 15 years.

Conclusion

Faster weight growth in early childhood is associated with asthma and bronchial hyperresponsiveness, and faster weight growth across childhood is associated with higher FVC and FEV₁ values.

Small for gestational age birth weight: impact on lung structure and function

Accumulating data suggest that prenatal compromises leading to intrauterine growth restriction (IUGR) increase the risk for respiratory deficiencies after birth. In this respect, a growing body of epidemiological evidence in infants, children and adults indicates that small for gestational (SGA) birth weight can adversely affect lung function, thus questioning the widely accepted concept that IUGR accelerates lung maturation and improves outcome. Although the mechanisms responsible for the relationship between SGA and later lung dysfunction remain poorly documented, animal data indicate that intrauterine lung development can be adversely affected by factors associated with IUGR, namely reduced substrate supply, fetal hypoxemia and hypercortisolemia. Thus, it is suggested that fetal adaptations to intrauterine undernutrition result in permanent changes in lung structure, which in turn lead to chronic airflow obstruction. The purpose of this review is to describe and discuss the effects of IUGR on lung structure and function.

[Intrauterine growth retardation and lung development]

Epidemiological studies have shown that intrauterine growth restriction is associated with increased respiratory morbidity in the neonatal period with an increased risk of bronchopulmonary dysplasia. Respiratory consequences of environmental intrauterine changes extend into childhood and adulthood with abnormal lung function tests. In animal models, changes in surfactant and alveolarization disorders vary from one study to another. Moreover, the molecular mechanisms involved are poorly understood. Fetal adaptations to intrauterine malnutrition result in permanent changes in lung structure, raising the question of lung "programming".

Long term respiratory consequences of intrauterine growth restriction

Epidemiological studies demonstrate that in-utero growth restriction and low birth weight are associated with impaired lung function and increased respiratory morbidity from infancy, throughout childhood and into adulthood. Chronic restriction of nutrients and/or oxygen during late pregnancy causes abnormalities in the airways and lungs of offspring, including smaller numbers of enlarged alveoli with thicker septal walls and basement membranes. The structural abnormalities and impaired lung function seen soon after birth persist or even progress with age. These changes are likely to cause lung symptomology through life and hasten lung aging.

Effects of maternal food restriction on offspring lung extracellular matrix deposition and long term pulmonary function in an experimental rat model

Intrauterine growth restriction (IUGR) increases the risk of respiratory compromise throughout postnatal life. However, the molecular mechanism(s) underlying the respiratory compromise in offspring following IUGR is not known. We hypothesized that IUGR following maternal food restriction (MFR) would affect extracellular matrix deposition in the lung, explaining the long-term impairment in pulmonary function in the IUGR offspring. Using a well-established rat model of MFR during gestation to produce IUGR pups, we found that at postnatal day 21, and at 9 months (9M) of age the expression and abundance of elastin and alpha smooth muscle actin (αSMA), two key extracellular matrix proteins, were increased in IUGR lungs when compared to controls (P < 0.05, n = 6), as determined by both Western and immunohistochemistry analyses. Compared to controls, the MFR group showed no significant change in pulmonary resistance at baseline, but did have significantly decreased pulmonary compliance at 9M (P < 0.05 vs. control, n = 5). In addition, MFR lungs exhibited increased responsiveness to methacholine challenge. Furthermore, exposing cultured fetal rat lung fibroblasts to serum deprivation increased the expression of elastin and elastin-related genes, which was blocked by serum albumin supplementation, suggesting protein deficiency as the predominant mechanism for increased pulmonary elastin deposition in IUGR lungs. We conclude that accompanying the changes in lung function, consistent with bronchial hyperresponsiveness, expression of the key alveolar extracellular matrix proteins elastin and αSMA increased in the IUGR lung, thus providing a potential explanation for the compromised lung function in IUGR offspring.

Fetal and infant growth and asthma symptoms in preschool children: the Generation R Study

RATIONALE

Low birth weight is associated with an increased risk of wheezing in childhood.

OBJECTIVES

We examined the associations of longitudinally measured fetal and infant growth patterns with the risks of asthma symptoms in preschool children.

METHODS

This study was embedded in a population-based prospective cohort study among 5,125 children. Second- and third-trimester fetal growth characteristics (head circumference, femur length, abdominal circumference, and weight) were estimated by repeated ultrasounds. Infant growth (head circumference, length, and weight) was measured at birth and at the ages of 3, 6, and 12 months. Parental report of asthma symptoms until the age of 4 years was yearly obtained by questionnaires.

MEASUREMENTS AND MAIN RESULTS

Both fetal restricted and accelerated growth, defined as a negative or positive change of more than 0.67 standard deviation score, were not associated with asthma symptoms until the age of 4 years. Accelerated weight gain from birth to 3 months following normal fetal growth was associated with increased risks of asthma symptoms (overall odds ratio for wheezing: 1.44 [95% confidence interval: 1.22, 1.70]; shortness of breath: 1.32 [1.12, 1.56]; dry cough: 1.16 [1.01, 1.34]; persistent phlegm: 1.30 [1.07, 1.58]), but not with eczema (0.95 [0.80, 1.14]). These associations were independent of other fetal growth patterns and tended to be stronger for children of atopic mothers than for children of nonatopic mothers.

CONCLUSIONS

Weight-gain acceleration in early infancy was associated with increased risks of asthma symptoms in preschool children, independent of fetal growth. Early infancy might be a critical period for the development of asthma.

Patterns of fetal and infant growth are related to atopy and wheezing disorders at age 3 years

BACKGROUND

Little is known about whether patterns of early growth are associated with altered respiratory and immune development. This study relates prenatal and infant growth patterns to wheeze and atopy at age 3&emsp14;years.

METHODS

Birth weight and length were measured in 1548 children born at term. Conditional fetal head and abdominal circumference growth velocities were calculated from antenatal ultrasound measurements. Conditional postnatal growth velocities were calculated from infant weight, length and adiposity data. Measures of size and conditional growth were related to parentally-reported infant and early childhood wheeze and to atopic status at age 3 years.

RESULTS

The risk of atopy increased by 46% per SD increase in abdominal circumference growth velocity from 11 to 19 weeks gestation but by 20% per SD decrease in abdominal growth velocity from 19 to 34 weeks (p=0.007 and p=0.011, respectively). The risk of atopic wheeze increased by 20% per SD decrease in 19-34-week abdominal growth (p=0.046). The risk of non-atopic wheeze increased by 10% per SD decrease in 11-19-week head circumference growth. Greater relative infant weight and adiposity gains were associated with both atopic and non-atopic wheeze.

CONCLUSIONS

A rapid growth trajectory during 11-19 weeks gestation followed by late gestation growth faltering is associated with atopy, suggesting that influences affecting fetal growth may also alter immune development. A lower early fetal growth trajectory is associated with non-atopic wheeze, possibly reflecting an association with smaller airways. An association between postnatal adiposity gain and wheeze may partly reflect prenatal influences that cause fetal growth to falter but are then followed by postnatal adiposity gain.

Perinatal stress and early life programming of lung structure and function

Exposure to environmental toxins during critical periods of prenatal and/or postnatal development may alter the normal course of lung morphogenesis and maturation, potentially resulting in changes that affect both structure and function of the respiratory system. Moreover, these early effects may persist into adult life magnifying the potential public health impact. Aberrant or excessive pro-inflammatory immune responses, occurring both locally and systemically, that result in inflammatory damage to the airway are a central determinant of lung structure-function changes throughout life. Disruption of neuroendocrine function in early development, specifically the hypothalamic-pituitary-adrenal (HPA) axis, may alter functional status of the immune system. Autonomic nervous system (ANS) function (sympathovagal imbalance) is another integral component of airway function and immunity in childhood. This overview discusses the evidence linking psychological factors to alterations in these interrelated physiological processes that may, in turn, influence childhood lung function and identifies gaps in our understanding.

Early intervention in management of very preterm growth-restricted fetuses: 2-year outcome of infants delivered on fetal indication before 30 gestational weeks

OBJECTIVES

To describe the outcome of growth-restricted fetuses with absent or reversed end-diastolic flow (ARED) in the umbilical artery delivered on fetal indication before 30 gestational weeks.

METHODS

Between 1998 and 2004, 42 fetuses with intrauterine growth restriction (IUGR) and ARED in the umbilical artery were delivered liveborn by Cesarean section on fetal indication before 30 gestational weeks. The median gestational age at delivery was 27 + 1 (range, 24 + 4 to 29 + 5) weeks. An additional four fetuses died in utero at a median gestational age of 24 + 2 (range, 23 + 5 to 25 + 4) weeks. Neonatal morbidity, infant mortality and major neurological morbidity of liveborn infants were compared with those in two control groups: all 371 liveborn infants delivered at < 30 weeks during the corresponding time period (Group A) and a subset of these, 42 matched infants without IUGR (Group B).

RESULTS

Thirty-two fetuses (76%) [corrected] were delivered within 48 h of the occurrence of ARED (25 absent, seven reversed end-diastolic flow). The remaining 10 fetuses (five absent, five reversed end-diastolic flow) were monitored for a median of 6.5 (range, 3-18) days before delivery. One infant died in the neonatal period and three during the first year of postnatal life (2-year survival 90%). The incidence of chronic lung disease was higher in the ARED Group than in Control Groups A and B (P = 0.001 and P = 0.03, respectively). There were no differences between the groups in the occurrence of necrotizing enterocolitis, cerebral hemorrhage or retinopathy of prematurity. Cerebral palsy was diagnosed in 14% of the index group compared with 11% and 17% of Control Groups A and B (P > 0.05).

CONCLUSIONS

Very preterm growth-restricted fetuses with umbilical artery ARED delivered on fetal indication, in most cases before the occurrence of severe changes in the ductus venosus velocity waveforms and/or fetal heart rate tracings, showed high 2-year survival and low morbidity.

Effect of maternal food restriction on fetal rat lung lipid differentiation program

Although "fetal programming" has been extensively studied in many organs, there is only limited information on pulmonary effects in the offspring following intrauterine growth restriction (IUGR). We aimed to determine the effects of nutrient restriction on the lung structure and lung lipid differentiation programs in offspring using an animal mode of maternal food restriction (MFR). We utilized a rodent model of 50% MFR from day 10 of gestation to term and then using lung morphology, Western blotting, Real Time RT-PCR and Oil Red O staining, lung structure and development of the offspring were examined at postnatal days (p) 1, p21, and 9 months (9M). At postnatal day 1, MFR pups weighed significantly less compared to control pups, but at p21 and 9M, they weighed significantly more. However, lung weight, expressed as a percentage of body weight between the two groups was not different at all time-points examined. The MFR group had significantly decreased alveolar number and significantly increased septal thickness at p1 and 9M, indicating significantly altered lung structure in the MFR offspring. Furthermore, although at p1, compared to the control group, lung lipid accumulation was significantly decreased in the MFR group, at 9M, it was significantly increased. There were significant temporal changes in the parathyroid hormone-related protein/peroxisome proliferator-activated receptor gamma signaling pathway and surfactant synthesis. We conclude that MFR alters fetal lung lipid differentiation programming and lung morphometry by affecting specific epithelial-mesenchymal signaling pathways, offering the possibility for specific interventions to overcome these effects.

Postnatal growth rate, but not mild preterm birth, influences airway structure in adult sheep challenged with house dust mite

The authors recently showed that preterm birth per se, in the absence of assisted ventilation or elevated inhaled oxygen levels, alters the structure of the airway walls in young lambs. The initial aim of the present study was to determine whether these changes persist into adulthood. Preterm (P; n = 7) lambs were delivered 14 days before term and compared with control lambs (C; n = 8) born at term ( approximately 147 days). After weaning, the sheep were kept as a flock with daily exposure to pasture until approximately 1.2 years old. All sheep were sensitized to house dust mite extract and then given aerosol challenges with house dust mite 10 to 12 weeks before autopsy. At autopsy, the right lung was fixed in neutral-buffered formalin at an inflation pressure of 20 cm H(2)O. The architecture of the walls of airway generations 4, 6, and 8 and the bronchioles was assessed by computer-aided image analysis of histological sections of airway walls cut in cross-section. Morphometric analysis showed that preterm birth per se had no significant effect on airway wall structure. Within both groups (preterm and term), we identified animals that grew at different growth rates after birth; a second aim, therefore, was to determine the influence of postnatal growth rates on airway structure at maturity. The 15 sheep were divided into 2 groups based on nonoverlapping growth rates between birth and 200 days of age: slower growing sheep (SG; n = 7) gained 102 +/- 5 g/day and faster growing sheep (FG; n = 8) gained 197 +/- 14 g/day (P < .01). In SG sheep, the pulmonary airways had thinner walls and less smooth muscle in relation to basement membrane perimeter. The airway epithelium was also thinner in the SG sheep. In the bronchiolar epithelium, there were fewer goblet cells and Clara cells in SG compared to FG sheep. We conclude that the early effects of preterm birth on the airway epithelium do not persist to maturity. However, slow growth after birth results in altered airway development, with effects persisting to maturity.

Early growth and adult respiratory function in men and women followed from the fetal period to adulthood

BACKGROUND

While some studies suggest that poor fetal growth rate, as indicated by lower birth weight, is associated with poor respiratory function in childhood, findings among adults remain inconsistent. A study was undertaken to determine the association between early growth and adult respiratory function.

METHODS

A longitudinal birth cohort study was performed of 5390 men and women born full term and prospectively followed from the fetal period to adulthood. Weight at birth and infancy were recorded, and forced expiratory volume in 1 s (FEV(1)) and forced vital capacity (FVC) were assessed by standard spirometry at age 31 years.

RESULTS

Adult FEV(1) and FVC increased linearly with higher birth weight in both men and women with no apparent threshold. After adjustment for sex, adult height and other potential confounders operating through the life course, every 500 g higher birth weight was associated with a higher FEV(1) of 53.1 ml (95% CI 38.4 to 67.7) and higher FVC of 52.5 ml (95% CI 35.5 to 69.4). These positive associations persisted across categories of smoking, physical activity and body mass index, with the lowest respiratory function noted among those with lower birth weight who were smokers, led a sedentary lifestyle or were overweight. Weight gain in infancy was also positively associated with adult lung function.

CONCLUSION

Birth weight is continuously and independently associated with adult respiratory function. It is plausible that poor growth in early life may restrict normal lung growth and development, which could have long-term consequences on lung function later in life.

Pulmonary function and structure following mild preterm birth in lambs

Our objective was to determine whether postnatal respiratory function, lung growth, and lung structure are affected by preterm birth which did not require neonatal respiratory support. Two groups of preterm (P) lambs were delivered 2 weeks before term, at 133 days of gestational age (GA). Tissue was collected at term equivalent age (TEA, 147 days GA) in one P group and at 6 weeks post-TEA in the other. Tissue was also collected from control (C) lambs soon after term birth (TEA) and at 6 weeks post-TEA. Lung function was assessed at TEA and 6 weeks post-TEA. Respiratory system compliance (Crs/kg BWT) was not different between P and C groups at TEA, but was higher (P = 0.02) in P lambs at 6 weeks post-TEA. Pulmonary resistance was 62% higher in P lambs than controls (P = 0.07) at TEA, and remained higher at 6 weeks post-TEA. Lung weights (wet and dry) were greater (P < 0.05) in preterm animals at both ages; when adjusted for body weight, only dry lung weight remained higher at 6 weeks post-TEA. Alveoli were more numerous (P = 0.05) and smaller (P = 0.05) in preterm lambs compared to controls at both ages. Alveolar septa were 33% thicker and the blood-air barrier was 26% thicker in P lambs than in controls at TEA, and remained thicker at 6 weeks post-TEA. In P lambs, the airway epithelium was thicker at TEA and 6 weeks post-TEA. At TEA, pulmonary tropoelastin expression was 27% lower in P lambs. At 6 weeks post-TEA, dry lung weight and lung protein content were approximately 50% greater in preterm lambs than in controls (P < 0.05), whereas lung DNA, elastin, and collagen contents were similar in the two groups. We conclude that mild preterm birth per se leads to both transient and persistent changes in lung development. Persistent increases in lung protein content and in the thickness of the airway epithelium, and a greater number of smaller alveolar, may alter later lung function.

Early developmental origins of impaired lung structure and function

Epidemiological studies show that exposure to factors that restrict fetal growth or lead to low birthweight can alter lung development and have later adverse effects on lung function and respiratory health. The major causal factors include reduced nutrient and oxygen availability, nicotine exposure via maternal tobacco smoking and preterm birth, each of which can affect critical stages of lung development. Experimental studies show that these environmental insults can permanently alter lung structure and hence lung function, increasing the risk of respiratory illness and accelerating the rate of lung aging. Further studies are required that address the molecular and cellular mechanisms by which these factors adversely affect lung development and whether such effects can be blocked or reversed. Ultimately however, a major goal should be to prevent prenatal compromises through clinical monitoring, and in the case of smoking through education, thereby ensuring that each fetus has the best possible environment in which to develop.

Effect of Nomega-nitro-L-arginine methyl ester-induced intrauterine growth restriction on postnatal lung growth in rats

Infants with intrauterine growth restriction (IUGR) are at high risk for morbidity and mortality. Preeclampsia, one of the leading causes of IUGR, begins during the canalicular phase of lung development. The aim of our study was to determine whether induced IUGR was responsible for abnormal lung development in rat pups. We randomized pregnant Sprague-Dawley rats to daily gavage with either the nitric oxide synthase inhibitor Nomega-nitro-L-arginine methyl ester (L-NAME; n = 5, 50 mg . kg(-1) . d(-1)) or pure water (n = 6). The pups were weighed at birth and on postnatal days 7 and 14. At each of these time points, pups were killed and their lung growth was assessed on the basis of lung volume and light-microscopy morphometric data. At birth, body weight, total alveolar surface area, and alveolar surface density were significantly decreased and alveolar size was significantly increased in the L-NAME group, compared with the control group. On day 7, body weight was similar in the two groups, and the only significant difference was smaller total alveolar surface area in the L-NAME group. On day 14, neither body weight nor lung morphometric parameters were significantly different between the L-NAME group and the controls. These results suggest that postnatal catch-up growth may completely correct the lung development disorders present at birth in IUGR pups, in parallel with the catch-up body weight gain.

Short-term outcome in infants with a birthweight less than 501 grams

AIM

To report survival and morbidity until discharge in preterm infants <501 g with life support started immediately after birth.

METHODS/STUDY DESIGN

Cohort study of all preterm infants with birthweights < 501 g born in three tertiary perinatal centres between 1 January 1998 and 31 December 2001 (gestational age (GA) 25.2 [21.0-30.7] wk; birthweight 435 [290-500] g; median [range]).

RESULTS

A total of 107 infants with birthweights <501 g were born. Twenty-nine were stillborn. A prenatal decision to initiate life support immediately after birth was reached in 9/37 (24%) infants <24.0 wk GA and in 39/42 (93%) infants > or =24.0 wk GA. Survival was 3/37 (8%) and 26/41 (63%) in infants <24 wk GA and > or =24.0 wk GA, respectively. Twenty-nine of the 48 infants with immediate life support (60%) survived (95% CI: 46-75%). Forty-two of these 48 (88%) infants were small for gestational age. No infant without immediate life support survived (0/30). Twenty-three (79%) survivors developed chronic lung disease (CLD) and eight (28%) received photocoagulation for retinopathy of prematurity (ROP).

CONCLUSION

In this population of extremely low birthweight infants, survival was higher than in previous studies when life support was provided immediately after birth. Short-term morbidity was similar to other studies. The presented data on survival support our concept to offer immediate life support after birth in preterm infants with birthweights <501 g. The long-term outcome of these infants needs to be assessed urgently.

Prematurity and intrauterine growth retardation--double jeopardy?

Premature infants born with IUGR are at a several-fold increased risk for mortality and major neonatal morbidities, including RDS, BPD, ROP, and NEC. These severe complications of prematurity are intensified by the effect of suboptimal fetal growth. The possible pathophysiologic processes initiated in utero and continuing after birth have been discussed. Recently reported data suggest that IUGR is a risk factor in programming for the later development of cardiovascular diseases, hypertension, and diabetes mellitus in adult life. Experimental research related to the pathophysiology and etiology of these conditions may enable appropriate intervention directed at reducing the excess risk associated with the short- and long-term mortality and morbidity among premature SGA infants.

Small size at birth and greater postnatal weight gain: relationships to diminished infant lung function

Recent evidence suggests that impaired lung development is linked with diminished lung function and an increased risk of chronic obstructive airway disease in adulthood. To examine environmental influences on early lung development, we measured lung function in 131 normal-term infants aged 5-14 weeks. Adjusting for age at measurement, FEV at 0.4 seconds fell by 4.4% for each standard deviation decrease in birth weight (p = 0.047); when adjusted for FVC, FEV at 0.4 seconds was not related to birth weight but fell by 3.2% per standard deviation increase in infant weight gain (p = 0.001). Age- and sex-adjusted total respiratory system compliance fell by 7.0% per standard deviation decrease in birth weight (p < 0.001) but was not related to infant weight gain. In univariate analyses, age-adjusted forced expiratory flow at functional residual capacity was not related to birth weight, but decreased by 11.0% per standard deviation increase in infant weight gain (p = 0.007). The respiratory rate rose by 5.1% per standard deviation increase in infant weight gain (p = 0.001). Lung function measurements were not related to infant feeding. The observations suggest that lower rates of fetal growth and higher rates of early infancy weight gain are associated with impaired lung development.

Chronic lung disease of prematurity and intrauterine growth retardation: a population-based study

OBJECTIVE

To determine the risk of chronic lung disease (CLD) in small for gestational age (SGA) preterm infants in comparison to appropriately grown and large for gestational age (LGA) infants.

METHODS

Observational study derived from a geographically defined population (Trent Health Region, United Kingdom). All preterm infants of <or=32 completed weeks' gestation born to Trent resident mothers admitted to neonatal units between 1995 and 1999 (inclusive) were included. Birth weight percentiles were created for the whole population, and infants were classified as SGA infants (if <10th percentile), appropriately grown (if between 25th and 75th percentiles-reference group), and LGA infants (if >or=90th centile). Both mortality and CLD rates (using both 28 days' and 36 weeks' postmenstrual age [PMA] definitions) were determined for these groups of infants.

RESULTS

Four thousand fifty-one preterm infants <or=32 weeks' gestation were identified. SGA infants showed higher mortality before 28 days' postnatal age and 36 weeks' PMA as compared with reference group infants (odds ratio [OR]: 2.01, 95% confidence interval [CI]: 1.49-2.72; and OR: 2.00, 95% CI: 1.49-2.69), respectively. SGA infants showed a significantly greater risk of developing CLD, both at 28 days' and 36 weeks' PMA as compared with the reference group infants (OR: 1.34, 95% CI: 1.03-1.74; and OR: 1.87, 95% CI: 1.39-2.51), respectively. LGA infants showed a trend toward a reduced incidence of CLD in comparison to the reference group, which was statistically significant for the 36 weeks' definition (OR: 0.76-28 weeks, 95% CI: 0.57-1.01; and OR: 0.55-36 weeks, 95% CI: 0.37-0.81).

CONCLUSIONS

Fetal growth seems to influence mortality in general and morbidity, attributable to CLD, in particular in preterm infants. SGA preterm infants are at higher risk of death before 28 days' and 36 weeks' PMA and CLD by both definitions. LGA infants show reduced risk of CLD.

Lung development-the effects of chronic hypoxia

Chronic hypoxia compromises the development of both airways and pulmonary vasculature following exposure before or after birth. It also impairs adaptation to extrauterine life. The immediate morbidity and mortality is high, and long-term sequelae in terms of lung structure, and thus function, are common, particularly in premature infants. Chronic lung disease or bronchopulmonary dysplasia can develop with or without cor pulmonale. The extensive fibrotic disease of classical bronchopulmonary dysplasia has become uncommon with the development of improved treatment strategies, but the development of the lung periphery can still be compromised as more immature babies survive. This article highlights the landmarks of normal lung development together with the principal established and newly recognized features of exposure to chronic hypoxic in the young. In doing so, it indicates promising areas for research activity.