Postnatal lung function after prenatal steroid treatment in sheep: effect of gender

Impact of sex, race, and social determinants of health on neonatal outcomes

Despite the global improvements in neonatal outcomes, mortality and morbidity rates among preterm infants are still unacceptably high. Therefore, it is crucial to thoroughly analyze the factors that affect these outcomes, including sex, race, and social determinants of health. By comprehending the influence of these factors, we can work towards reducing their impact and enhancing the quality of neonatal care. This review will summarize the available evidence on sex differences, racial differences, and social determinants of health related to neonates. This review will discuss sex differences in neonatal outcomes in part I and racial differences with social determinants of health in part II. Research has shown that sex differences begin to manifest in the early part of the pregnancy. Hence, we will explore this topic under two main categories: (1) Antenatal and (2) Postnatal sex differences. We will also discuss long-term outcome differences wherever the evidence is available. Multiple factors determine health outcomes during pregnancy and the newborn period. Apart from the genetic, biological, and sex-based differences that influence fetal and neonatal outcomes, racial and social factors influence the health and well-being of developing humans. Race categorizes humans based on shared physical or social qualities into groups generally considered distinct within a given society. Social determinants of health (SDOH) are the non-medical factors that influence health outcomes. These factors can include a person's living conditions, access to healthy food, education, employment status, income level, and social support. Understanding these factors is essential in developing strategies to improve overall health outcomes in communities.

The Impact of Infant Sex on Multiple Courses versus a Single Course of Antenatal Corticosteroids: A Secondary Analysis of a Randomized Controlled Trial

OBJECTIVE

 Animal literature has suggested that the impact of antenatal corticosteroids (ACS) may vary by infant sex. Our objective was to assess the impact of infant sex on the use of multiple courses versus a single course of ACS and perinatal outcomes.

STUDY DESIGN

 We conducted a secondary analysis of the Multiple Courses of Antenatal Corticosteroids for Preterm Birth trial, which randomly allocated pregnant people to multiple courses versus a single course of ACS. Our primary outcome was a composite of perinatal mortality or clinically significant neonatal morbidity (including neonatal death, stillbirth, severe respiratory distress syndrome, intraventricular hemorrhage [grade III or IV], cystic periventricular leukomalacia, and necrotizing enterocolitis [stage II or III]). Secondary outcomes included individual components of the primary outcome as well as anthropometric measures. Baseline characteristics were compared between participants who received multiple courses versus a single course of ACS. An interaction between exposure to ACS and infant sex was assessed for significance and multivariable regression analyses were conducted with adjustment for predefined covariates, when feasible.

RESULTS

 Data on 2,300 infants were analyzed. The interaction term between treatment status (multiple courses vs. a single course of ACS) and infant sex was not significant for the primary outcome (p = 0.86), nor for any of the secondary outcomes (p > 0.05).

CONCLUSION

 Infant sex did not modify the association between exposure to ACS and perinatal outcomes including perinatal mortality or neonatal morbidity or anthropometric outcomes. However, animal literature indicates that sex-specific differences after exposure to ACS may emerge over time and thus investigating long-term sex-specific outcomes warrants further attention.

KEY POINTS

· We explored the impact of infant sex on perinatal outcomes after multiple versus a single course of ACS.. · Infant sex was not a significant effect modifier of ACS exposure and perinatal outcomes.. · Animal literature indicates that sex-specific differences after ACS exposure may emerge over time.. · Further investigation of long-term sex-specific outcomes is warranted..

The impact of gender medicine on neonatology: the disadvantage of being male: a narrative review

This narrative non-systematic review addresses the sex-specific differences observed both in prenatal period and, subsequently, in early childhood. Indeed, gender influences the type of birth and related complications. The risk of preterm birth, perinatal diseases, and differences on efficacy for pharmacological and non-pharmacological therapies, as well as prevention programs, will be evaluated. Although male newborns get more disadvantages, the physiological changes during growth and factors like social, demographic, and behavioural reverse this prevalence for some diseases. Therefore, given the primary role of genetics in gender differences, further studies specifically targeted neonatal sex-differences will be needed to streamline medical care and improve prevention programs.

Influence of antenatal corticosteroids and sex on the mortality and morbidity of extremely prematurely born infants

OBJECTIVE

To report the effect of antenatal corticosteroids (ANS) on mortality, intraventricular hemorrhage (IVH), bronchopulmonary dysplasia (BPD) and the duration of ventilation according to sex in extremely preterm infants.

METHODS

All extremely preterm infants admitted to any neonatal unit in England between 2014 and 2019.

RESULTS

Eleven thousand seven hundred and fourteen infants (54% male) were included with a median (IQR) gestational age of 26 + 1 (24 + 6 - 27 + 1) weeks, birth weight of 809 (670 - 960) grams and birth weight z-score of -0.38 (-0.88 to 0.07). ANS were administered in 10,449 infants (89%); equally in males and females. Infants who received ANS compared to those who did not, had a lower mortality before discharge (18.7 versus 32.3%, p < .001), a lower incidence of IVH grade III-IV (14.5 versus 25.5%, p < .001) and a shorter median (IQR) duration of mechanical ventilation [10 (3-27) versus 13 (5-31) days, p < .001]. Female compared to male infants had a lower mortality (18.7 versus 21.7%, p < .001), a lower incidence of IVH grade III-IV (10.9 versus 13.9%, p < .001), a lower incidence of bronchopulmonary dysplasia (61.6 versus 68.2%, p= <.001) and a shorter median (IQR) duration of mechanical ventilation days [9 (3-26) versus 13 (4-29) days, p= <.001]. In females, the risk of dying before discharge from hospital was greater in those who did not receive ANS (odds ratio (OR) 1.81, 95% CI 1.35-2.44) than in those who did (OR 0.55, 95% CI 0.41-0.74). In males the risk of dying was also greater in those that did not receive ANS (OR 1.36, 95% CI 1.03-1.77) compared to those who did (OR 0.74, 95% CI 0.57-0.96).

CONCLUSION

Antenatal corticosteroids had a greater beneficial effect in female compared to male extremely prematurely born infants in reducing death before discharge.

Low-dose antenatal betamethasone treatment achieves preterm lung maturation equivalent to that of the World Health Organization dexamethasone regimen but with reduced endocrine disruption in a sheep model of pregnancy

BACKGROUND

The intramuscular administration of antenatal steroids to women at risk of preterm delivery achieves high maternal and fetal plasma steroid concentrations, which are associated with adverse effects and may reduce treatment efficacy. We have demonstrated that antenatal steroid efficacy is independent of peak maternofetal steroid levels once exposure is maintained above a low threshold.

OBJECTIVE

This study aimed to test, using a sheep model of pregnancy, whether the low-dose antenatal steroid regimen proposed as part of the Antenatal Corticosteroids for Improving Outcomes in Preterm Newborns trial would achieve preterm lung maturation equivalent to that of the existing World Health Organization dexamethasone treatment regimen, but with reduced risk of adverse outcomes.

STUDY DESIGN

Following ethical review and approval, date-mated ewes with single fetuses received intramuscular injections of either (1) four 6-mg maternal intramuscular injections of dexamethasone phosphate every 12 hours (n=22), (2) 4 2-mg maternal intramuscular injections of betamethasone phosphate every 12 hours (n=21), or (3) 4 2-mL maternal intramuscular injections of saline every 12 hours (n=16). Of note, 48 hours after first injection, (124±1 day), lambs were delivered, ventilated for 30 minutes, and euthanized for sampling. Arterial blood gas, respiratory, hematological, and biochemical data were analyzed for between-group differences with analysis of variance according to distribution and variance, with P<.05 taken as significant.

RESULTS

After 30 minutes of ventilation, lambs from both steroid-treated groups had significant and equivalent improvements in lung function relative to saline control (P<.05). There was no significant difference in arterial blood pH, pO₂, pCO₂, lung compliance, ventilator efficiency index, or lung volume at necropsy with a static pressure of 40 cmH₂O. The messenger RNA expression of surfactant protein (Sp)a, Spb, Spc, Spd, aquaporin (Aqp)1, Aqp5, and sodium channel epithelial 1 subunit beta (Scnn1b) was equivalent between both steroid groups. Maternal and fetal plasma neutrophil, glucose, and fetal plasma C-peptide levels were significantly elevated in the dexamethasone group, relative to the betamethasone group. Fetal plasma insulin-like growth factor 1 was significantly reduced in the dexamethasone group compared with the betamethasone group (P<0.05). Fetal adrenocorticotropic hormone (r=0.53), maternal glucose value (r=-0.52), and fetal glucose values (r=-0.42) were correlated with maternal weight in the betamethasone group (P<.05), whereas fetal pCO₂ and pO₂ were not correlated. There was no significant difference between male and female lamb outcomes in any groups for any of the items evaluated.

CONCLUSION

This study reported that in preterm lambs, a low-dose treatment regimen of 8 mg betamethasone achieves lung maturation equivalent to that of a 24-mg dexamethasone-based regimen, but with smaller perturbations to the maternofetal hypothalamic-pituitary-adrenal axis. These data suggested that given steroid pharmacokinetic differences between sheep and humans, a betamethasone dose of 2 mg may remain above the minimum dose necessary for robust maturation of the preterm lung. Maternal weight-adjusted betamethasone doses might also be a key to reducing perturbations to the maternofetal hypothalamic-pituitary-adrenal axis.

Y It Matters—Sex Differences in Fetal Lung Development

Within this review, sex-specific differences in alveolar epithelial functions are discussed with special focus on preterm infants and the respiratory disorders associated with premature birth. First, a short overview about fetal lung development, the challenges the lung faces during perinatal lung transition to air breathing and respiratory distress in preterm infants is given. Next, clinical observations concerning sex-specific differences in pulmonary morbidity of human preterm infants are noted. The second part discusses potential sex-specific causes of pulmonary complications, including pulmonary steroid receptors and local lung steroid metabolism. With regard to pulmonary steroid metabolism, it is important to highlight which steroidogenic enzymes are expressed at which stage during fetal lung development. Thereafter, we review the knowledge concerning sex-specific aspects of lung growth and maturation. Special focus is given to alveolar epithelial Na+ transport as a driver of perinatal lung transition and the sex differences that were noted in this process.

Sex differences in modulation of fetoplacental vascular resistance in growth-restricted mouse fetuses following betamethasone administration: comparisons with human fetuses

BACKGROUND

Maternally administered corticosteroids are routinely used to accelerate fetal lung maturation in pregnancies at risk of early preterm delivery. Although, among the subgroup with growth restriction, a majority show a temporary improvement in umbilical artery Doppler waveforms that may be sustained up to 7 days, a minority will acutely decompensate in response to corticosteroids in association with deteriorating umbilical and fetal Doppler waveforms. The basis for such acute Doppler changes is presently unknown. Our group has developed a noninvasive ultrasound methodology to measure wave reflections in the umbilical artery and have established that wave reflection metrics are sensitive to structural changes in the placental vasculature and to acute changes in vascular tone. Using this approach, we demonstrated in healthy pregnant mice that fetoplacental vascular resistance decreased in betamethasone-treated mice compared with saline-treated controls.

OBJECTIVE

This study aimed to investigate the effects of betamethasone administration on the wave reflection metrics in a mouse model of fetal growth restriction and to compare these findings with equivalent measurements in human fetuses.

STUDY DESIGN

Pregnant CD-1 mice were housed from embryonic day 14.5 to embryonic day 17.5 in either a normoxic (21% O₂, n=24) or hypoxic environment (11% O₂, n=22), the latter being an established mouse model of fetal growth restriction. To investigate the effect of maternally administered betamethasone on the fetoplacental vasculature, ultrasound imaging was performed at baseline and 4 hours after treatment (either betamethasone or sterile saline). Umbilical artery wave reflection metrics were compared between the groups and for the effect of fetal sex. In addition, a cohort of 10 pregnant women with elevated umbilical artery pulsatility index and evidence of fetal growth restriction and 6 controls were imaged before and after corticosteroid administration.

RESULTS

In the mouse model, after betamethasone administration, the female fetuses from the hypoxia group showed a 15% increase in umbilical artery diameter, a 98% increase in umbilical artery blood flow, and a 27% decrease in umbilical artery reflection coefficient, whereas the males from the hypoxia group showed no substantial changes. In agreement with our mouse findings, umbilical artery reflections were found to be larger in human growth-restricted fetuses than controls in women at risk of preterm birth.

CONCLUSION

Our studies provide insight into the mechanism whereby the human growth-restricted fetus may exhibit a temporary favorable fetoplacental vascular response to maternally administered corticosteroids. Further investigations are needed to understand why the male growth-restricted fetus seems unable to mount this favorable vascular response.

Effect of maternal betamethasone administration on feto-placental vascular resistance in the mouse†

Antenatal corticosteroids are often administered to women at risk of preterm birth to accelerate fetal lung development; however, there is evidence that this treatment may adversely affect placental function in some fetuses. Our group has recently demonstrated that wave reflections in the umbilical artery (UA), measured using high-frequency ultrasound, are sensitive to placental vascular abnormalities. In the present study, we used this approach to investigate the effect of maternal administration of betamethasone, a clinically relevant corticosteroid, on the feto-placental vasculature of the mouse. Fetuses were assessed at embryonic day (E)15.5 and E17.5 in C57BL6/J mice. At both gestational ages, the UA diameter, UA blood flow, and the wave reflection coefficient were significantly elevated in the betamethasone-treated mice compared to vehicle-treated controls. These observations support the interpretation that placental vascular resistance dropped with betamethasone treatment to an extent that could not be explained by vasodilation of the UA alone. Consistent with clinical studies, the effect of betamethasone on UA end-diastolic velocity was heterogeneous. Our results suggest that UA wave reflections are more sensitive to acute changes in placental vascular resistance compared with the UA pulsatility index, and this technique may have clinical application to identify a favorable placental vascular response to fetal therapies such as antenatal corticosteroids, where the fetal heart rate is likely to vary.

Antenatal PPAR-γ agonist pioglitazone stimulates fetal lung maturation equally in males and females

Antenatal steroids (ANS) accelerate fetal lung maturation and reduce the incidence of respiratory distress syndrome. However, sex specificity, i.e., being less effective in males, and potential long-term neurodevelopmental sequelae, particularly with repeated courses, remain significant limitations. The differential sex response to ANS is likely mediated via the inhibitory effect of fetal androgens on steroid's stimulatory effect on alveolar epithelial-mesenchymal interactions. Since peroxisome proliferator-activated receptor-γ (PPAR-γ) agonists accelerate lung maturation by stimulating alveolar epithelial-mesenchymal interactions, independent of fetal sex, we hypothesized that the effect of PPAR-γ agonist pioglitazone (PGZ) would be sex-independent. Pregnant Sprague-Dawley rat dams were intraperitoneally administered dexamethasone (DEX) or PGZ on embryonic day (e) 18 and e19. At e20, pups were delivered by cesarean section, and fetal lungs and brains were examined for markers of lung maturation and apoptosis, respectively. Mixed epithelial-fibroblast cell cultures were examined to gain mechanistic insights. Antenatal PGZ increased alveolar epithelial and mesenchymal maturation markers equally in males and females; in contrast, antenatal DEX had sex-specific effects. Additionally, unlike DEX, antenatal PGZ did not increase hippocampal apoptosis. We conclude that PPAR-γ agonist administration is an effective, and probably even a superior, alternative to ANS for accelerating fetal lung maturity equally in both males and females.

Glucocorticoids Equally Stimulate Epithelial Na+ Transport in Male and Female Fetal Alveolar Cells

Preterm infants frequently suffer from respiratory distress syndrome (RDS), possibly due to lower expression of epithelial Na⁺ channels (ENaC). RDS incidence is sex-specific, affecting males almost twice as often. Despite the use of antenatal glucocorticoids (GCs), the sex difference persists. It is still controversial whether both sexes benefit equally from GCs. We previously showed that Na⁺ transport is higher in female compared with male fetal distal lung epithelial (FDLE) cells. Since GCs increase Na⁺ transport, we hypothesized that their stimulating effect might be sex-specific. We analyzed FDLE cells with Ussing chambers and RT-qPCR in the presence or absence of fetal serum. In serum-free medium, GCs increased the ENaC activity and mRNA expression, independent of sex. In contrast, GCs did not increase the Na⁺ transport in serum-supplemented media and abolished the otherwise observed sex difference. Inhibition of the GC receptor in the presence of serum did not equalize Na⁺ transport between male and female cells. The GC-induced surfactant protein mRNA expression was concentration and sex-specific. In conclusion, female and male FDLE cells exhibit no sex difference in response to GCs with regard to Na⁺ transport, and GR activity does not contribute to the higher Na⁺ transport in females.

The efficacy of antenatal steroid therapy is dependent on the duration of low-concentration fetal exposure: evidence from a sheep model of pregnancy

BACKGROUND

Antenatal corticosteroids are among the most important and widely used interventions to improve outcomes for preterm infants. Antenatal corticosteroid dosing regimens remain unoptimized and without maternal weight-adjusted dosing. We, and others, have hypothesized that, once a low concentration of maternofetal steroid exposure is achieved and maintained, the duration of the steroid exposure determines treatment efficacy. Using a sheep model of pregnancy, we tested the relationship among steroid dose, duration of exposure, and treatment efficacy.

OBJECTIVE

The study was conducted to investigate the relative importance of duration and magnitude of fetal corticosteroid exposure to mature the preterm fetal ovine lung.

STUDY DESIGN

Ewes with single fetuses at 120 days gestation received an intravenous bolus (loading dose) followed by a maintenance infusion of betamethasone phosphate to target 12-hour fetal plasma betamethasone concentrations of (1) 20 ng/mL, (2) 10 ng/mL, or (3) 2 ng/mL. In a subsequent experiment, fetal plasma betamethasone concentrations were targeted at 2 ng/mL for 26 hours. Negative control animals received sterile saline solution. Positive control animals received 2 intramuscular injections of 0.25 mg/kg Celestone Chronodose (betamethasone phosphate + betamethasone acetate) spaced at 24 hours. Preterm lambs were delivered surgically and ventilated 48 hours after treatment commenced. Maternal and fetal plasma betamethasone concentrations were confirmed by mass spectrometry in a parallel study of chronically catheterized, corticosteroid-treated ewes and fetuses.

RESULTS

The loading and maintenance doses were achieved and maintained the desired fetal plasma betamethasone concentrations of approximately 20, 10, and 2 ng/mL for 12 hours. Compared with the 12-hour infusion-treated animals, lambs from the positive control (2 intramuscular doses of 0.25 mg/kg Celestone Chronodose) group had the greatest functional lung maturation (compliance, gas exchange, arterial pH) and molecular evidence of maturation (glucocorticoid receptor signaling activation), despite having maximum fetal plasma betamethasone concentrations 2.5 times lower than animals in the 20 ng/mL betamethasone infusion group. Lambs from the 12-hour 2-ng/mL betamethasone infusion group had little functional lung maturation. In contrast, lambs from the 26-hour 2-ng/mL betamethasone infusion group had functional lung maturation equivalent to lambs from the positive control group.

CONCLUSION

In preterm lambs that were exposed to antenatal corticosteroids, high maternofetal plasma betamethasone concentrations did not correlate with improved lung maturation. The largest and most consistent improvements in lung maturation were in animals that were exposed to either the clinical course of Celestone Chronodose or a low-dose betamethasone phosphate infusion to achieve a fetal plasma betamethasone concentration of approximately 2 ng/mL for 26 hours. The duration of low-concentration maternofetal steroid exposure, not total dose or peak drug exposure, is a key determinant for antenatal corticosteroids efficacy. These findings underscore the need to develop an optimized steroid dosing regimen that may improve both the efficacy and safety of antenatal corticosteroids therapy.

Vitamin A Protects the Preterm Lamb Diaphragm Against Adverse Effects of Mechanical Ventilation

Background: Preterm infants are deficient in vitamin A, which is essential for growth and development of the diaphragm. Preterm infants often require mechanical ventilation (MV) for respiratory distress. In adults, MV is associated with the development of ventilation-induced diaphragm dysfunction and difficulty weaning from the ventilator. We assessed the impact of MV on the preterm diaphragm and the protective effect of vitamin A during MV.

Methods: Preterm lambs delivered operatively at ∼131 days gestation (full gestation: 150 days) received respiratory support by synchronized intermittent mandatory ventilation for 3 days. Lambs in the treated group received daily (24 h) enteral doses of 2500 IU/kg/day vitamin A combined with 250 IU/kg/day retinoic acid (VARA) during MV, while MV control lambs received saline. Unventilated fetal reference lambs were euthanized at birth, without being allowed to breathe. The fetal diaphragm was collected to quantify mRNA levels of myosin heavy chain (MHC) isoforms, atrophy genes, antioxidant genes, and pro-inflammatory genes; to determine ubiquitin proteasome pathway activity; to measure the abundance of protein carbonyl, and to investigate metabolic signaling.

Results: Postnatal MV significantly decreased expression level of the neonatal MHC gene but increased expression level of MHC IIx mRNA level (p < 0.05). Proteasome activity increased after 3 days MV, accompanied by increased MuRF1 mRNA level and accumulated protein carbonyl abundance. VARA supplementation decreased proteasome activity and FOXO1 signaling, down-regulated MuRF1 expression, and reduced reactive oxidant production.

Conclusion: These findings suggest that 3 days of MV results in abnormal myofibrillar composition, activation of the proteolytic pathway, and oxidative injury of diaphragms in mechanically ventilated preterm lambs. Daily enteral VARA protects the preterm diaphragm from these adverse effects.

Immune function? A missing link in the gender disparity in preterm neonatal outcomes

INTRODUCTION

In neonatology, males exhibit a more severe disease course and poorer prognosis in many pathological states when compared to females. Perinatal brain injury, respiratory morbidity, and sepsis, among other complications, preferentially affect males. Preterm neonates (born <37 weeks gestation) display a particularly marked sexual disparity in pathology, especially at the borders of viability. The sex biases in preterm neonatal outcomes and underlying multifactorial mechanisms have been incompletely explored. Sex-specific clinical phenomena may be partially explained by intrinsic differences in immune function. The distinct immune system of preterm neonates renders this patient population vulnerable, and it is increasingly important to consider biological sex in disease processes and to strive for improved outcomes for both sexes. Areas covered: We discuss the cellular responses and molecular intermediates in immune function which are strongly dependent on sex-specific factors such as the genetic and hormonal milieu of premature birth and consider novel findings in a clinical context. Expert commentary: The role of immune function in the manifestation of sex-specific disease manifestations and outcomes in preterm neonates is a critical prognostic variable. Further mechanistic elucidation will yield valuable translational and clinical information of disease processes in preterm neonates which may be harnessed for modulation.

Influence of Sex on Gestational Complications, Fetal-to-Neonatal Transition, and Postnatal Adaptation

Fetal sex is associated with striking differences during in utero development, fetal-to-neonatal transition, and postnatal morbidity and mortality. Male sex fetuses are apparently protected while in utero resulting in a higher secondary sex rate for males than for females. However, during fetal-to-neonatal transition and thereafter in the newborn period, female exhibits a greater degree of maturation that translates into a better capacity to stabilize, less incidence of prematurity and prematurity-associated morbidities, and better long-term outcomes. The present review addresses the influence of sex during gestation and postnatal adaptation that includes the establishment of an adult-type circulation, the initiation of breathing, endurance when confronted with perinatal hypoxia ischemia, and a gender-related different response to drugs. The intrinsic mechanisms explaining these differences in the perinatal period remain elusive and further experimental and clinical research are therefore stringently needed if an individual oriented therapy is to be developed.

Surfactant phospholipid composition of gastric aspirate samples differs between male and female very preterm infants

BackgroundAmong preterm infants, males have a greater incidence of respiratory distress and death than do females born at the same gestational age, likely due to sex-related differences in lung maturation. Our aim was to determine whether surfactant phospholipid composition differs between male and female preterm infants.MethodsGastric aspirate samples from male and female infants born between 25 and 30 weeks of gestation at The Royal Women's Hospital, Melbourne, Australia, were collected within 1 h after birth. Phospholipid composition was analyzed by electrospray ionization tandem mass spectrometry.ResultsPreterm males had higher proportions of total phosphatidylinositol (PI) and phosphatidylserine 36:2, lower proportions of total sphingomyelin (S) and S 33:1 and 35:1, and a greater phosphatidylcholine (PC)/S ratio than did females. The proportions of PC 30:0, PC 34:0, PC 34:2, PC 36:2, PC 36:3, and PC 38:2 differed between the sexes at different gestational weeks of birth; the proportion of PC 32:0 (dipalmitoylphosphatidylcholine) in males was lower than that in females at 25 weeks of gestation but higher at 27 weeks.ConclusionPhospholipid composition in pulmonary surfactant is different between male and female preterm infants of the same gestational age, which may contribute to the increased risk for respiratory morbidities in one sex.

Biological sex and the risk of cerebral palsy in Victoria, Australia

AIM

Males typically outnumber females in cerebral palsy (CP) cohorts. To better understand this 'male disadvantage' and provide insight into causal pathways to CP, this study used 1983 to 2009 Australian CP and population birth cohorts to identify associations and trends with respect to biological sex and CP.

METHOD

Within birth gestation groups, sex ratios were calculated to evaluate any male excess in the CP cohort compared with livebirths, neonatal deaths, neonatal mortality and survival rates, neonatal survivors, and CP rates in survivors. Sex- and gestation-specific trends in neonatal mortality, CP rates, and CP sex ratios were assessed by plotting their annual frequencies and fitting quadratic curves.

RESULTS

Over-representation of males in preterm live births partly explained the male excess in the CP cohort after preterm birth, especially at 28 to 31 weeks. Higher CP rates in male neonatal survivors also contributed to the male excess in CP, particularly at <28 and 37+ weeks. Higher neonatal mortality rates in males at all gestations had little impact on the CP sex ratio. There was no clearly discernible change over time in the CP sex ratio.

INTERPRETATION

Gestation-specific associations between sex and CP provide insight into causal pathways to CP and suggest sex-specific differences in response to neuroprotective strategies.

The clinical use of corticosteroids in pregnancy

BACKGROUND

The use of antenatal steroid therapy is common in pregnancy. In early pregnancy, steroids may be used in women for the treatment of recurrent miscarriage or fetal abnormalities such as congenital adrenal hyperplasia. In mid-late pregnancy, the antenatal administration of corticosteroids to expectant mothers in anticipation of preterm birth is one of the most important advances in perinatal medicine; antenatal corticosteroids are now standard care for pregnancies at risk of premature delivery in high- and middle-income countries. The widespread uptake of this therapy is due to a compelling body of evidence demonstrating improved neonatal outcomes following antenatal corticosteroid exposure, stemming most notably from corticosteroid-driven maturation of fetal pulmonary function. As we approach the 50th anniversary of landmark work in this area by Liggins and Howie, it is apparent that much remains to be understood with regards to how we might best apply antenatal corticosteroid therapy to improve pregnancy outcomes at both early and mid to late gestation.

METHODS

Drawing on advances in laboratory science, pre-clinical and clinical studies, we performed a narrative review of the scientific literature to provide a timely update on the benefits, risks and uncertainties regarding antenatal corticosteroid use in pregnancy. Three, well-established therapeutic uses of antenatal steroids, namely recurrent miscarriage, congenital adrenal hyperplasia and preterm birth, were selected to frame the review.

RESULTS

Even the most well-established antenatal steroid therapies lack the comprehensive pharmacokinetic and dose-response data necessary to optimize dosing regimens. New insights into complex, tissue-specific corticosteroid signalling by genomic-dependent and independent mechanisms have not been used to inform corticosteroid treatment strategies. There is growing evidence that some fetal corticosteroid treatments are either ineffective, or may result in adverse outcomes, in addition to lasting epigenetic changes in a variety of homeostatic mechanisms. Nowhere is the need to better understand the intricacies of corticosteroid therapy better conveyed than in the findings of Althabe and colleagues who recently reported an increase in overall neonatal mortality and maternal morbidity in association with antenatal corticosteroid administration in low-resource settings.

CONCLUSIONS

New research to clarify the benefits and potential risks of antenatal corticosteroid therapy is urgently needed, especially with regard to corticosteroid use in low-resource environments. We conclude that there is both significant scope and an urgent need for further research-informed refinement to the use of antenatal corticosteroids in pregnancy.

Does lung development differ in male and female fetuses?

Preterm male infants have a higher incidence of morbidity and mortality due to respiratory insufficiency than females of the same gestational age. This male disadvantage could be due to differences in lung architecture; however, few studies have compared lung architecture in male and female fetuses during late gestation. Our principal objectives were to compare the morphology of the fetal lung and the maturity of the surfactant system in preterm male and female fetuses. Lungs from male (n = 9) and female (n = 11) fetal sheep were collected at 0.9 of term (131 days of the 145-day gestation) for morphological and molecular analyses. In separate groups, tracheal liquid was obtained from male (n = 9) and female (n = 9) fetuses at 0.9 of term for determination of surfactant phospholipid composition. We found no sex-related differences in body weight, lung weight, right lung volume, lung tissue and airspace fractions, mean linear intercept, septal crest density, septal thickness, the proportion of proliferating and apoptotic cells, and the percentages of collagen or elastin. The gene expression of surfactant protein -A, -B, -C, and -D and tropoelastin was similar between sexes. There were no differences in the proportion of the major phospholipid classes in the tracheal liquid between sexes; however there was a significantly higher percentage of the phospholipid species phosphatidylinositol 38:5 in males. The greater morbidity and mortality in preterm male lambs do not appear to be related to differences in lung structure or surfactant phospholipid synthesis before birth, but may relate to physiological adaptation to air-breathing at birth.

Glucocorticoid metabolism in the developing lung: adrenal-like synthesis pathway

Glucocorticoids (GCs) are essential to normal lung development. They participate in the regulation of important developmental events including morphological changes, and lung maturation leading to the surge of surfactant synthesis by type II epithelial cells. Antenatal GC is administered to mothers at risk of premature delivery to reduce the risk of respiratory distress syndrome (RDS). Sex differences were reported in RDS, in the efficiency of antenatal GC treatment independently of surfactant levels, and in surfactant lipid synthesis. Type II epithelial cell maturation is regulated by epithelial-fibroblast cell-cell communication and involves paracrine factors secreted by fibroblasts under the stimulatory effect of GC. This positive action of GC can be inhibited by androgens through the androgen receptor (AR) present in fibroblasts. In fact, lung development is regulated not only by GC and androgens but also by GC and androgen metabolisms within the developing lung. We recently reviewed the metabolism of androgens in the fetal lung [45]. Here, we review multiple aspects of GC metabolism in the developing lung including inactivation and re-activation by 11β-HSDs, synthesis from the adrenal-like synthesis pathway expressed within the lung and the putative role of CRH and ACTH originating from lung in the regulation of this pathway. This article is part of a Special Issue entitled 'Pregnancy and Steroids'.

Double exposure to intra-amniotic lipopolysaccharide and maternal betamethasone induces sustained increase of neutrophils in the lungs and disrupts alveolarization in newborn rats

AIM

We investigated the combined effects of intra-amniotic lipopolysaccharide (LPS) and maternal betamethasone (BMZ) on alveolarization using a newborn rat model.

METHODS

LPS (1.0 μg/sac) or vehicle was injected into the amniotic sacs of pregnant rats and BMZ (170 μg/kg) or vehicle was injected intramuscularly into the pregnant rats twice at 8-h intervals on gestation day 20. The rat pups were delivered spontaneously after 2-2.5 days and raised until the measurements were taken. Bronchoalveolar lavage was performed on days 2 and 5, and morphometric analyses of the lungs were performed on days 5 and 14.

RESULTS

Intra-amniotic LPS significantly increased the neutrophils in the bronchoalveolar lavage fluid (BALF) on day 2, but double exposure to LPS and BMZ significantly alleviated the neutrophil increase in the BALF. On day 5, while the neutrophils in the BALF decreased in the animals exposed to LPS alone, the neutrophil numbers in the BALF were steady in the animals exposed to both LPS and BMZ. Morphometric analyses on days 5 and 14 revealed a significant disruption of alveolarization only in the animals exposed to both LPS and BMZ.

CONCLUSIONS

Our results suggested that double exposure to maternal BMZ and intra-amniotic LPS induces sustained increase of neutrophils in the lungs and disrupts alveolarization.

Placental P-glycoprotein is unaffected by timing of antenatal glucocorticoid therapy but reduced in SGA preterm infants

INTRODUCTION

The beneficial effects of antenatal glucocorticoid therapy on fetal lung maturation require their passage across the placental glucocorticoid barrier, composed of glucocorticoid metabolising enzymes, such as 11 beta hydroxysteroid dehydrogenase (11βHSD), and proteins that efflux glucocorticoids, such as P-glycoprotein (P-gp). We have shown that 11βHSD2 activity is responsive to antenatal glucocorticoids, however the effect on placental P-gp remains unknown. Since antenatal glucocorticoids have a greater prophylactic effect in females compared to males, we also assessed whether this therapy induced sexually dimorphic effects on P-gp expression, as well as on placental inflammatory processes mediated by corticosteroids.

METHODS

Placentas were collected from 53 women presenting in threatened preterm labour, and processed to assess cytokine and P-gp mRNA expression, as well as P-gp localisation using immunohistochemistry.

RESULTS

Placental cytokine, P-gp mRNA and protein expression were not altered by timing of antenatal glucocorticoids or fetal sex. However, both P-gp mRNA and protein expression were significantly reduced in placentas from infants born small for gestational age (SGA) compared to appropriately grown infants (p < 0.05), suggesting a role for P-gp in its pathogenesis via the provision of a net increase in fetal exposure to bioactive exogenous glucocorticoids.

CONCLUSIONS

While this study identified no change in placental P-gp following antenatal glucocorticoids, it has provided evidence that P-gp plays an important role in cases of SGA. This supports the known mechanistic relationship between antenatal glucocorticoids, fetal development and the postnatal phenotype. Given that P-gp also confers fetal protection from a number of drugs, this finding warrants further investigation to improve clinical management of the SGA fetus.

Sex differences in cardiorespiratory transition and surfactant composition following preterm birth in sheep

Male preterm infants are at greater risk of respiratory morbidity and mortality than females but mechanisms are poorly understood. Our objective was to identify the basis for the “male disadvantage” following preterm birth using an ovine model of preterm birth in which survival of females is greater than males. At 0.85 of term, fetal sheep underwent surgery (11 female, 10 male) for the implantation of vascular catheters to monitor blood gases and arterial pressure. After cesarean delivery at 0.90 of term, lambs were monitored for 4 h while spontaneously breathing; lambs were then euthanized and static lung compliance measured. We analyzed surfactant phospholipid composition in amniotic fluid and in bronchoalveolar lavage fluid (BALF) taken at necropsy; we also analyzed surfactant protein ( SP) expression in lung tissue. Before delivery male fetuses tended to have lower pH ( P = 0.052) compared with females. One hour after delivery, males had significantly lower pH and higher arterial partial pressure of CO2 (PaCO2), lactate, glucose, and mean arterial pressure than females. Two males died 1 h after birth. Static lung compliance was 37% lower in males than females ( P < 0.05). In BALF, males had significantly more protein, a lower percentage of the phosphatidylcholine (PC) 32:0 (dipalmitoylphosphatidylcholine) and higher percentages of PC34:2 and PC36:2. There were no sex-related differences in lung architecture or expression of SP-A, -B, -C, and -D. The lower lung compliance in male preterm lambs compared with females may be due to altered surfactant phospholipid composition and function. These changes may compromise gas exchange and impair respiratory adaptation after male preterm birth.

The cardiopulmonary haemodynamic transition at birth is not different between male and female preterm lambs

Males born preterm are at greater risk of illness and death than females, principally due to respiratory disease. Much of the excess morbidity occurs within the first few hours of life. Therefore, the aim of the present study was to investigate whether or not differences in the cardiopulmonary transition soon after birth underlie the increased morbidity in males after preterm birth. Nine female and thirteen male lambs (128±2 days gestation) underwent surgery immediately before delivery for implantation of a pulmonary arterial flow-probe and catheters into the main pulmonary artery and a carotid artery. After birth lambs were ventilated for 30 min (tidal volume 7 mL kg(-1)) while anaesthetised. Arterial pressures and flows were recorded in real time and left-ventricular output measured using Doppler echocardiography. Before birth, fetal cardiopulmonary haemodynamics, arterial blood gases, pH, glucose and lactate did not differ between sexes. Similarly, in the neonatal period there were no significant differences in arterial blood gas status, ventilation parameters, respiratory indices or cardiopulmonary haemodynamics between the sexes. Our data show that the cardiopulmonary transition at birth in ventilated, anaesthetised preterm lambs is not influenced by sex. Thus, the neonatal 'male disadvantage' is not explained by an impaired cardiovascular transition at birth.

Ultra-high dose of intra-amniotic or direct fetal intramuscular betamethasone for lung maturation in the preterm goat model

OBJECTIVE

To evaluate the effects of intra-amniotic (IA) and fetal injections of a single ultra-high dose of betamethasone (BM) 48 h before preterm delivery on neonatal pulmonary function, using an experimental goat model.

STUDY DESIGN

Eighteen date-mated singleton pregnant Hair goats were randomized into four groups. At gestational day 118 (alveolar phase, term 150-155 days) after obtaining a sample of amniotic fluid, fetuses in group 1 (n=5) received 8 mg/kg IA BM, and in group 2 (n=5) 4 mg/kg fetal IM BM. In group 3 (n=4) (0.3mg/kg/day) maternal BM was administered at day 118 and 119 with a 24h interval; control fetuses (n=4) received 1 mL/kg of IA saline at day 118. At gestational day 120, after obtaining second sample of amniotic fluids 18 kids were delivered by preterm cesarean section, entubated, weighed, and mechanically ventilated for 15 min. Arterial blood gas samples and deflation/inflation lung pressure-volume measurements were obtained. After sacrifice, lungs were removed, weighed, gross examined and processed for further histological and immunohistochemical (IHC) evaluations. On hematoxylin and eosin (HE) stained slides, presence and severity of lung emphysema was evaluated; slides stained for surfactant proteins, and caspases were used for semi-quantitative evaluation of lung maturation. Kruskal-Wallis, Mann-Whitney, Wilcoxon signed rank, and chi-square tests were used for comparisons.

RESULTS

IA BM was associated with increased number of stillbirths (60% vs. 0% in control) (p=0.06) and emphysematous changes. Bodyweight-adjusted pressure-volume measurements were improved after maternal, but not IA or fetal, BM (p=0.06). Following mechanical ventilation, arterial blood gas parameters did not significantly alter across maternal and fetal administrations. However, pH was significantly lower (p<0.05) and carbon dioxide partial pressure was higher (p<0.05) in the control group, indicating hypercapnic acidemia in non-treated pregnancies. None of the treatments induced measurable alterations in amniotic fluid lecithin/sphingomyelin (L/S) values. IA and fetal routes were associated with decreased surfactant protein expressions and increased apoptotic activity in alveolar and bronchio-alveolar epithelial cells.

CONCLUSION

Ultra-high dose IA and fetal IM BM is not superior to the standard dose and maternal way of administration in our experimental design.

Prenatal programming of the innate immune response following in utero exposure to inflammation: a sexually dimorphic process?

Maternal infection and inflammation are common events during pregnancy. This article documents evidence that suggests such inflammation compromises the development of the fetal innate immune response, in support of an in utero origins hypothesis of neonatal and childhood inflammatory disease. The potential for this response to exhibit sex specificity is also explored, based on evidence of sexually dimorphic placental responses to maternal inflammation.

The influence of sex and antenatal betamethasone exposure on vasoconstrictors and the preterm microvasculature

OBJECTIVE

Dysregulated vascular resistance contributes to hypotension following preterm birth with sex-specific differences in microvascular function conferring a male disadvantage. We hypothesized that glucocorticoid mediated, sex-specific differences in the endogenous catecholamine norepinephrine and endothelially derived endothelin-1 (ET-1) contribute to microvascular dysfunction in preterm neonates in the immediate newborn period.

METHODS

Umbilical and plasma ET-1 and normetanephrine, in 24 h urine samples, were determined at 24, 72, and 120 h of age in 24-34 week infants (n = 60). Microvascular blood flow was determined by laser Doppler flowmetry.

RESULTS

In infants born within 72 h of antenatal glucocorticoid exposure, normetanephrine was higher in females than males (p = 0.048). Normetanephrine was inversely correlated with both microvascular blood flow at 24 h (p = 0.025) and CRIB II (p = 0.001). While umbilical arterial ET-1 was higher in females delivered <72 h after antenatal betamethasone (p = 0.006), plasma ET-1 did not correlate with microvascular blood flow or illness severity. Only sex and normetanephrine contributed significantly to both microvascular blood flow and endothelium dependant vasodilatation.

CONCLUSIONS

These data support glucocorticoid mediated, sex-specific differences in mediators of vascular tone that may contribute to the impaired mechanisms compromising successful hemodynamic adaption to neonatal life and resulting in excess male morbidity and mortality.

Induced preterm birth in sheep: a suitable model for studying the developmental effects of moderately preterm birth

Our aim was to characterize an ovine model of preterm birth that allows analysis of the developmental effects of preterm birth in the absence of postnatal confounding factors. Preterm birth was induced at 131 days of gestation in 82 lambs; controls (n = 31) were born at term (145 days). Overall survival of preterm lambs was 60%; males had significantly lower survival than females (44% vs 76%); 94% of term lambs survived. Although the birth weight of preterm lambs was approximately 0.9 kg lower than in term lambs, the crown-to-rump and forelimb lengths were similar. At 9 weeks after term-equivalent age, there were no differences in body weight or dimensions between preterm and term lambs; when adjusted for body weight, the heart was 21% heavier in preterm than term lambs. We conclude that moderately preterm birth in sheep is characterized by a greater survival of female lambs than males and has significant effects on organ development.

Sex-specific alterations in placental 11β-hydroxysteroid dehydrogenase 2 activity and early postnatal clinical course following antenatal betamethasone

Placental 11β-hydroxysteroid dehydrogenase-2 (11βHSD2) limits fetal glucocorticoid exposure and is associated with physiological stability in the premature newborn infant. Antenatal betamethasone alters 11βHSD2 activity and confers sex-specific advantages in neonatal outcome. We investigated the influence of betamethasone and sex on 11βHSD2 activity, neonatal adrenal function and clinical course in 24- to 36-wk gestation neonates from birth to day 5 of life. Univariate analyses demonstrated an interaction between timing of betamethasone exposure and sex for 11βHSD2 activity rate ( P = 0.02) and umbilical arterial cortisol ( P = 0.01). For infants born < 72 h following antenatal betamethasone, females had higher 11βHSD2 activity ( P < 0.01) and umbilical arterial cortisol ( P = 0.01) than males. Females born < 72 h of betamethasone exposure had higher day 1 urinary cortisol, if exposed to perinatal stress, than males ( P < 0.01). For infants born < 72 h after betamethasone exposure, 11βHSD2 activity was negatively correlated with Clinical Illness Severity Score score ( r = −0.79 P = 0.01) and positively correlated with mean arterial blood pressure ( r = 0.8 P = 0.01) only in females. Sex-specific placental 11BHSD2 autoregulation following antenatal betamethasone exposure may limit adrenal suppression in females influencing physiological stability following preterm birth. A lack of adjustment in 11βHSD2 and adrenal response may contribute to the increased incidence of poor outcome observed in preterm males.

Sex differences in cell proliferation and glucocorticoid responsiveness in the zebra finch brain

Neural proliferation is a conserved property of the adult vertebrate brain. In mammals, stress reduces hippocampal neuronal proliferation and the effect is stronger in males than in females. We tested the effects of glucocorticoids on ventricular zone cell proliferation in adult zebra finches where neurons are produced that migrate to and incorporate within the neural circuits controlling song learning and performance. Adult male zebra finches sing and have an enlarged song circuitry; females do not sing and the song circuit is poorly developed. Freshly prepared slices from adult males and females containing the lateral ventricles were incubated with the mitotic marker BrdU with or without steroid treatments. BrdU-labeled cells were revealed immunocytochemically and all labeled cells within the ventricular zone were counted. We identified significantly higher rates of proliferation along the ventricular zone of males than in females. Moreover, acute administration of corticosterone significantly reduced proliferation in males with no effects in females. This effect in males was replicated by RU-486, which appears to act as an agonist of the glucocorticoid receptor in the songbird brain. The corticosterone effect was reversed by Thiram, which disrupts corticosterone action on the glucocorticoid receptor. Sex differences in proliferation and responses to stress hormones may contribute to the sexually dimorphic and seasonal growth of the neural song system of songbirds.

Preterm male infants need more initial respiratory support than female infants

Female infants have a significantly greater chance of surviving than male infants at similar birthweights and gestational ages, and have an advantage over males for a better outcome with less morbidity.

CONCLUSION

The exact mechanisms responsible for the gender differences, with a better chance of survival of female infants, remain to be determined. The paper by Elsmén et al. provides an important contribution to this most important area of clinical research.

Lung Morphometry after Repetitive Antenatal Glucocorticoid Treatment in Preterm Sheep

Antenatal glucocorticoids are thought to be less effective when delivery occurs more than 7 d after initiation of treatment; therefore, repeat courses are often administered. We examined lung structure after single or repetitive antenatal glucocorticoid injections in fetal sheep. Pregnant ewes received single or repetitive doses of 0.5 mg/kg betamethasone at 7-d intervals by maternal or fetal injection, beginning at D104 or D114 with delivery at D125, D135, or D146 gestation (term = 150 d). Changes in lung structure were more pronounced after repetitive versus single injections. Repetitive fetal or maternal injections beginning at D104 (delivery at D125) resulted in comparable structural changes: alveolar volume increased by 50 to 80%, alveolar numerical density decreased by 30 to 40%, and pleural and interlobular septal volumes decreased by as much as 70%. Similar changes were seen in animals delivered at D135 after repetitive maternal injections beginning at D114. There were no structural differences between control and repetitive betamethasone animals when delivery was delayed until D146, indicating that betamethasone induced structural changes were reversible.

Increased fetal glucocorticoid exposure delays puberty onset in postnatal life

The fetal environment is now recognized as a key determinant of the adult phenotype, being linked to development of diseases, including hypertension, as well as the timing of puberty. Such links may be related, in part, to the level of fetal exposure to maternal glucocorticoids in utero, which is normally regulated by placental expression of the enzyme 11beta-hydroxysteroid dehydrogenase (11beta-HSD). The present study examined whether manipulation of fetal glucocorticoid exposure, either directly or indirectly via 11beta-HSD inhibition, influences the subsequent timing of puberty. Administration of dexamethasone acetate at low (LDEX, 0.25 microg/ml drinking water) or high doses (HDEX, 1 microg/ml) or carbenoxolone (CBX, 2 x 10 mg/day, sc; an inhibitor of 11beta-HSD) to pregnant rats from day 13 to term (day 23) reduced offspring birthweight (LDEX: 9%; HDEX: 27%; CBX: 8%) and resulted in a subsequent delay in the onset of puberty in females (control: 41.4 +/- 0.5; LDEX: 44.8 +/- 0.7; HDEX: 48.5 +/- 0.4; CBX: 43.6 +/- 0.5 days). Importantly, the effects of CBX were not observed in the absence of maternal adrenals, indicating that they were mediated by increased fetal exposure to endogenous maternal glucocorticoids. In contrast, maternal treatment with metyrapone (MET; an inhibitor of glucocorticoid synthesis; 500 microg/ml drinking water from day 13) increased birthweight by 5% and advanced puberty onset in male offspring (control: 48.8 +/- 1.0; MET: 45.7 +/- 0.8 days). Changes in the timing of puberty onset were not attributable to changes in either bodyweight at puberty or peripubertal plasma leptin concentrations. Peripubertal plasma LH was also unaffected in animals with delayed puberty but was elevated in male offspring of MET-treated mothers. Collectively, these results demonstrate that fetal glucocorticoid exposure is an important determinant of the timing of puberty onset in postnatal life, and that this effect is operable within the normal physiological range of glucocorticoid concentrations.

Effects of antenatal endotoxin and glucocorticoids on the lungs of preterm lambs

OBJECTIVE

We hypothesized that the proinflammatory response to intra-amniotic endotoxin would induce lung maturation in preterm lambs.

STUDY DESIGN

Ewes were randomly assigned to receive 20 mg Escherichia coli endotoxin by intra-amniotic injection, maternal betamethasone (0.5 mg/kg), or sodium chloride solution. Preterm lambs were delivered at 125 days' gestation and underwent ventilation to assess lung function. Lung gas volume, surfactant concentrations, and inflammation were subsequently evaluated, with data analyzed by analysis of variance.

RESULTS

Fetal endotoxin exposure 6 days before delivery increased compliance by 59%, increased lung gas volume 2.3-fold, increased concentrations of surfactant lipids, increased surfactant A and B protein levels, and increased messenger ribonucleic acid expressions for surfactant proteins (all P <.01, vs control group). Betamethasone exposure resulted in less consistent effects. White blood cell counts were increased in fetal membranes and lungs after endotoxin exposure, but there was no severe inflammation.

CONCLUSION

A single fetal exposure to endotoxin resulted in large improvements in postnatal lung function and increases in surfactant concentrations after preterm delivery. These effects were qualitatively larger than those achieved with betamethasone.