The duration of fetal antenatal steroid exposure determines the durability of preterm ovine lung maturation

Antenatal corticosteroids: an updated assessment of anticipated benefits and potential risks

Antenatal steroid therapy is increasingly central to the obstetrical management of women at imminent risk of preterm birth. For women likely to deliver between 24 and 34 weeks' gestation, antenatal steroid therapy is the standard of care, conferring sizable benefits and few risks in high-resource environments when appropriately targeted. Recent studies have focused on antenatal steroid use in periviable and late preterm populations, and in term cesarean deliveries. As a result, antenatal steroid therapy has now been applied from 22 to 39+6 weeks of estimated gestational age. There is also an increased appreciation that the vast majority of randomized control data informing the use of antenatal steroids are derived from predominantly high-resource, White populations. Accordingly, a sizable amount of work has recently been undertaken to test how to safely use antenatal steroids in low- and middle-resource environments, wherein the often high rates of preterm birth make these low-cost, easily administered interventions an attractive proposition. It is likely underappreciated by the obstetrical and neonatal communities that the overall efficacy of antenatal steroid therapy is highly variable (including when preterm risk is accurately assessed), the treatment regimens used are largely arbitrary, dosing is suprapharmacologic for effect, and the benefit-risk balance is significantly and differentially modified by gestation. It is also very likely that the patients consenting to receive these treatments are similarly unaware of the complex balance of potential benefits and harms. Although a small number of follow-up studies present a generally benign picture of long-term antenatal steroid risk, several large, population-based retrospective studies have identified associations between antenatal steroid use, childhood mental disease, and newborn infections that warrant urgent attention. Of particular contemporary importance are emergent efforts to optimize antenatal steroid regimens on the basis of the pharmacokinetics and pharmacodynamics of the agents themselves, the need for better targeting of these potent drugs, and clear articulation of the potential benefits and harms of antenatal steroid use at differing stages of pregnancy and in different delivery contexts.

A comparison of 2 doses of antenatal dexamethasone for the prevention of respiratory distress syndrome: an open-label, noninferiority, pragmatic randomized trial

BACKGROUND

Antenatal corticosteroids have been used for the prevention of respiratory complications, intraventricular hemorrhage, necrotizing enterocolitis, and other adverse neonatal outcomes for over 50 years, with limited evidence about their optimal doses. Higher steroid doses or frequencies of antenatal corticosteroids in preterm newborns pose adverse effects such as prolonged adrenal suppression, negative effects on fetal programming and metabolism, and increased risks of neurodevelopmental and neuropsychological impairments. Conversely, lower doses of antenatal corticosteroids may be an effective alternative to induce fetal lung maturation with less risk to the fetus. Late preterm births represent the largest population of all preterm neonates, with a respiratory distress syndrome risk of 8.83%. Therefore, determining the optimal antenatal corticosteroid dosage is of particular importance for this population.

OBJECTIVE

This study aimed to compare the efficacy of 5-mg and 6-mg dexamethasone in preventing neonatal respiratory distress syndrome in women with preterm births at 320 to 366 weeks of gestation.

STUDY DESIGN

This was an open-label, randomized, controlled, noninferiority trial. Singleton pregnant women (n=370) at 320 to 366 weeks of gestation with spontaneous preterm labor or preterm premature rupture of membranes were enrolled. They were randomly assigned (1:1) to a 5-mg or 6-mg dexamethasone group. Dexamethasone was administered intramuscularly every 12 hours for 4 doses or until delivery. The primary outcome was the reduction in neonatal respiratory distress syndrome cases, whereas the secondary outcomes were any adverse maternal or neonatal events.

RESULTS

Between December 2020 and April 2022, 370 eligible women, anticipating deliveries within the gestational range of 32 0/7 to 36 6/7 weeks, willingly participated in the study. They were evenly split, with 185 women assigned to the 5-mg group and 185 to the 6-mg group. The study revealed that the demographic profiles of the participants in the 2 groups were remarkably similar, with no statistically significant disparities (P>.05). It is noteworthy that most of these women gave birth after 34 weeks of gestation. Despite a substantial proportion not completing the full course of steroid treatment, the 5-mg dose exhibited noninferiority compared with the 6-mg dose of dexamethasone, as indicated by a modest proportional difference of 0.5% (95% confidence interval, -2.8 to 43.9). Neonatal respiratory distress syndrome occurred in a relatively low percentage of newborns in both groups, affecting 2.2% in the 5-mg group and 1.6% in the 6-mg group. Notably, the risk difference of 0.6% fell comfortably within the predefined noninferiority threshold of 10%.

CONCLUSION

Our study suggests that a 5-mg dexamethasone dose is noninferior to a standard 6-mg dose in preventing neonatal respiratory distress syndrome in preterm births.

Respiratory benefit in preterm lambs is progressively lost when the concentration of fetal plasma betamethasone is titrated below two nanograms per milliliter

Antenatal steroid therapy is the standard of care for women at imminent risk of preterm delivery. Current dosing regimens use suprapharmacological doses to achieve extended fetal steroid exposures. We aimed to determine the lowest fetal plasma betamethasone concentration sufficient to achieve functional preterm lung maturation. Ewes with single fetuses underwent surgery to install a fetal jugular catheter. Adopting a stepwise design, ewes were randomized to either a saline-only group (negative control group; n = 9) or one of four betamethasone treatment groups. Each betamethasone group fetus received a fetal intravenous infusion to target a constant plasma betamethasone level of either 1) 2 ng/mL (2 ng/mL positive control group, n = 9); 2) 1 ng/mL, (1 ng/mL group, n = 10); 3) 0.5 ng/mL (0.5 ng/mL group, n = 10); or 4) 0.25 ng/mL (0.25 ng/mL group, n = 10). Fetuses were infused for 48 h, delivered, and ventilated. The positive control group, negative control group, and mid-point 0.5 ng/mL group animals were tested first. An interim analysis informed the final betamethasone group tested. Positive control group animals had large, statistically significant improvements in respiratory function. Based on an interim analysis, the 1.0 ng/mL group was studied in favor of the 0.25 ng/mL group. Treatment efficacy was progressively lost at plasma betamethasone concentrations lower than 2 ng/mL. We demonstrated that the acute respiratory benefit conveyed by antenatal steroid exposure in the fetal sheep is progressively lost when constant fetal plasma betamethasone concentrations are reduced below a targeted value of 2 ng/mL.NEW & NOTEWORTHY Lung maturation benefits in preterm lambs were progressively lost when fetal plasma betamethasone concentrations fell below 2 ng/mL. The effective floor threshold for a robust, lung-maturing exposure likely lies between 1 and 2 ng betamethasone per milliliter of plasma. Hypothalamic pituitary adrenal axis signaling and immunocyte populations remained materially disrupted at subtherapeutic steroid concentrations. These data demonstrate the potential to improve antenatal steroid therapy using reduced dose regimens informed by glucocorticoid pharmacokinetics and pharmacodynamics.

A Reduction in Antenatal Steroid Dose Was Associated with Reduced Cardiac Dysfunction in a Sheep Model of Pregnancy

Despite widespread use, dosing regimens for antenatal corticosteroid (ACS) therapy are poorly unoptimized. ACS therapy exerts a programming effect on fetal development, which may be associated with an increased risk of cardiovascular disease. Having demonstrated that low-dose steroid therapy is an efficacious means of maturing the preterm lung, we hypothesized that a low-dose steroid exposure would exert fewer adverse functional and transcriptional changes on the fetal heart. We tested this hypothesis using low-dose steroid therapy (10 mg delivered to the ewe over 36 h via constant infusion) and compared cardiac effects with those of a higher dose treatment (30 mg delivered to the ewe over 24 h by intramuscular injection; simulating currently employed clinical ACS regimens). Fetal cardiac function was assessed by ultrasound on the day of ACS treatment initiation. Transcriptomic analyses were performed on fetal myocardial tissue. Relative to saline control, fetuses in the higher-dose clinical treatment group had significantly lower ratios between early diastolic ventricular filling and ventricular filling during atrial systole, and showed the differential expression of myocardial hypertrophy-associated transcripts including βMHC, GADD45γ, and PPARγ. The long-term implications of these changes remain unstudied. Irrespective, optimizing ACS dosing regimens to maximize respiratory benefit while minimizing adverse effects on key organ systems, such as the heart, offers a means of improving the acute and long-term outcomes associated with this important obstetric therapy.

On optimal timing of antenatal corticosteroids: time to reformulate the question

Administration of antenatal corticosteroids (ACS) for accelerating foetal lung maturation in threatened preterm birth is one of the cornerstones of prevention of neonatal mortality and morbidity. To identify the optimal timing of ACS administration, most studies have compared subgroups based on treatment-to-delivery intervals. Such subgroup analysis of the first placebo-controlled randomised controlled trial indicated that a one to seven day interval between ACS administration and birth resulted in the lowest rates of neonatal respiratory distress syndrome. This efficacy window was largely confirmed by a series of subgroup analyses of subsequent trials and observational studies and strongly influenced obstetric management. However, these subgroup analyses suffer from a methodological flaw that often seems to be overlooked and potentially has important consequences for drawing valid conclusions. In this commentary, we point out that studies comparing treatment outcomes between subgroups that are retrospectively identified at birth (i.e. after randomisation) may not only be plagued by post-randomisation confounding bias but, more importantly, may not adequately inform decision making before birth, when the projected duration of the interval is still unknown. We suggest two more formal interpretations of these subgroup analyses, using a counterfactual framework for causal inference, and demonstrate that each of these interpretations can be linked to a different hypothetical trial. However, given the infeasibility of these trials, we argue that none of these rescue interpretations are helpful for clinical decision making. As a result, guidelines based on these subgroup analyses may have led to suboptimal clinical practice. As an alternative to these flawed subgroup analyses, we suggest a more principled approach that clearly formulates the question about optimal timing of ACS treatment in terms of the protocol of a future randomised study. Even if this 'target trial' would never be conducted, its protocol may still provide important guidance to avoid repeating common design flaws when conducting observational 'real world' studies using statistical methods for causal inference.

Effect of antenatal corticosteroid administration-to-birth interval on maternal and newborn outcomes: a systematic review

Background

Antenatal corticosteroids (ACS) are highly effective at improving outcomes for preterm newborns. Evidence suggests the benefits of ACS may vary with the time interval between administration-to-birth. However, the optimal ACS administration-to-birth interval is not yet known. In this systematic review, we synthesised available evidence on the relationship between ACS administration-to-birth interval and maternal and newborn outcomes.

Methods

This review was registered with PROSPERO (CRD42021253379). We searched Medline, Embase, CINAHL, Cochrane Library, Global Index Medicus on 11 Nov 2022 with no date or language restrictions. Randomised and non-randomised studies of pregnant women receiving ACS for preterm birth where maternal and newborn outcomes were reported for different administration-to-birth intervals were eligible. Eligibility screening, data extraction and risk of bias assessment were performed by two authors independently. Fetal and neonatal outcomes included perinatal and neonatal mortality, preterm birth-related morbidity outcomes and mean birthweight. Maternal outcomes included chorioamnionitis, maternal mortality, endometritis, and maternal intensive care unit admission.

Findings

Ten trials (4592 women; 5018 neonates), 45 cohort studies (at least 22,992 women; 30,974 neonates) and two case-control studies (355 women; 360 neonates) met the eligibility criteria. Across studies, 37 different time interval combinations were identified. There was considerable heterogeneity in included administration-to-birth intervals and populations. The odds of neonatal mortality, respiratory distress syndrome and intraventricular haemorrhage were associated with the ACS administration-to-birth interval. However, the interval associated with the greatest improvements in newborn outcomes was not consistent across studies. No reliable data were available for maternal outcomes, though odds of chorioamnionitis might be associated with longer intervals.

Intepretation

An optimal ACS administration-to-birth interval likely exists, however variations in study design limit identification of this interval from available evidence. Future research should consider advanced analysis techniques such as individual patient data meta-analysis to identify which ACS administration-to-birth intervals are most beneficial, and how these benefits can be optimised for women and newborns.

Funding

This study was conducted with funding support from the UNDP-UNFPA-UNICEF-WHO-World Bank Special Programme of Research, Development and Research Training in Human Reproduction (HRP), Department of Sexual and Reproductive Health and Research (SRH), a co-sponsored programme executed by the World Health Organization.

Antenatal corticosteroid administration-to-birth interval and neonatal outcomes in very preterm infants: A secondary analysis based on a prospective cohort study

INTRODUCTION

Despite the prevalent use of antenatal corticosteroids (ACS) to prevent preterm infants' adverse neonatal complications, there is currently no consensus on administration-to-birth intervals of ACS. International guidelines broadly agree that the administration of antenatal corticosteroids should be within 7 days prior to preterm birth. However, there is little evidence to support narrower optimal ACS administration-to-birth interval time. This study was undertaken to investigate the association between the administration-to-birth interval of ACS which is bounded by 48 hours and neonatal outcomes in very preterm infants.

MATERIALS AND METHODS

This is a single-center prospective observational study. Data were collected prospectively from eligible infants from January 2008 to April 2014 at the Santa Clara Valley Medical Center, neonatal outcomes were compared between two groups based on the interval of antenatal corticosteroid administration-to-birth: the interval of <48h, and the interval of >48h. It was noted that the entire study was completed by Dongli Song et al., and uploaded the data to the DATADRYAD website. The author only used this data for secondary analysis.

RESULTS

After adjusting potential confounders (gestational age, sex, birth weight, duration of cord clamping and delivery mode), the interval of >48h group compared to the interval of <48h group had significant reductions in mortality (OR: 0.17; 95% CI: 0.05-0.59), any retinopathy of prematurity (OR: 0.36; 95% CI: 0.16-0.82), severe retinopathy of prematurity (OR: 0.07; 95% CI: 0.01-0.45), any intubation (OR: 0.39; 95% CI: 0.20-0.75) and higher 1 min Apgar (β: 0.56; 95% CI: 0.10-1.02).

CONCLUSION

This study shows that in very preterm infants, compared with the interval of ACS<48h, the interval of ACS>48 hours has a significant health promotion effect.

The complex challenge of antenatal steroid therapy nonresponsiveness

Antenatal steroid therapy is standard care for women at imminent risk of preterm delivery. When deliveries occur within 7 days of treatment, antenatal steroid therapy reduces the risk of neonatal death and improves preterm outcomes by exerting diverse developmental effects on the fetal organs, in particular the preterm lung and cardiovascular system. There is, however, sizable variability in antenatal steroid treatment efficacy, and an important percentage of fetuses exposed to antenatal steroid therapy do not respond sufficiently to derive benefit. Respiratory distress syndrome, for example, is a central metric of clinical trials to assess antenatal steroid outcomes. In the present analysis, we addressed the concept of antenatal steroid nonresponsiveness, and defined a failed or suboptimal response to antenatal steroids as death or a diagnosis of respiratory distress syndrome following treatment. For deliveries at 24 to 35 weeks' gestation, the number needed to treat to prevent 1 case of respiratory distress syndrome was 19 (95% confidence interval, 14-28). Reflecting gestation-dependent risk, for deliveries at >34 weeks' gestation the number needed to treat was 55 (95% confidence interval, 30-304), whereas for elective surgical deliveries at term this number was 106 (95% confidence interval, 61-421). We reviewed data from clinical and animal studies investigating antenatal steroid therapy to highlight the significant incidence of antenatal steroid therapy nonresponsiveness (ie, residual mortality or respiratory distress syndrome after treatment), and the potential mechanisms underpinning this outcome variability. The origins of this variability may be related to both the manner in which the therapy is applied (ie, the treatment regimen itself) and factors specific to the individual (ie, genetic variation, stress, infection). The primary aims of this review were: (1) to emphasize to the obstetrical and neonatal communities the extent of antenatal steroid response variability and its potential impact; (2) to propose approaches by which antenatal steroid therapy may be better applied to improve overall benefit; and (3) to stimulate further research toward the empirical optimization of this important antenatal therapy.

Continuous but not pulsed low-dose fetal betamethasone exposures extend the durability of antenatal steroid therapy

Antenatal steroid (ANS) therapy is standard care for women at imminent risk of preterm labor. Despite extensive and long-standing use, 40-50% of babies exposed antenatally to steroids do not derive benefit; remaining undelivered 7d or more after ANS treatment is associated with a lack of treatment benefit, and increased risk of harms. We used a pregnant sheep model to evaluate the impact of continuous vs. pulsed ANS treatments on fetal lung maturation at an extended, eight-day treatment to delivery interval. Continuous low-dose ANS treatments for more than 72 hours in duration improved fetal lung maturation at eight days after treatment initiation. If fetal ANS exposure was interrupted, the beneficial ANS effect was lost. Truncated treatments, including that simulating the current clinical treatment regimen, did not improve lung function. Variable fetal lung maturation was correlated to the amount of saturated phosphatidylcholine present in the lung fluid. These data demonstrate that: i) the durability of ANS therapy may be enhanced by employing an extended, low-dose treatment regimen with reducing total dose; and ii) interrupting the continuity of fetal exposure by allowing it to fall below a minimal threshold was associated with comparably poor functional maturation of the preterm ovine lung.

Betamethasone phosphate reduces the efficacy of antenatal steroid therapy and is associated with lower birthweights when administered to pregnant sheep in combination with betamethasone acetate

BACKGROUND

Antenatal corticosteroid therapy is a standard of care for women at imminent risk of preterm labor. However, the optimal (maximum benefit and minimal risk of side effects) antenatal corticosteroid dosing strategy remains unclear. Although conveying overall benefit when given to the right patient at the right time, antenatal corticosteroid treatment efficacy is highly variable and is not risk-free. Building on earlier findings, we hypothesized that when administered in combination with slow-release betamethasone acetate, betamethasone phosphate and the high maternal-fetal betamethasone concentrations it generates are redundant for fetal lung maturation.

OBJECTIVE

Using an established sheep model of prematurity and postnatal ventilation of the preterm lamb, we aimed to compare the pharmacodynamic effects of low-dosage treatment with betamethasone acetate only against a standard dosage of betamethasone phosphate and betamethasone acetate as recommended by the American College of Obstetricians and Gynecologists for women at risk of imminent preterm delivery between 24 0/7 and 35 6/7 weeks' gestation.

STUDY DESIGN

Ewes carrying a single fetus at 122±1 days' gestation (term=150 days) were randomized to receive either (1) maternal intramuscular injections of sterile saline (the saline negative control group, n=12), (2) 2 maternal intramuscular injections of 0.25 mg/kg betamethasone phosphate+betamethasone acetate administered at 24-hour dosing intervals (the betamethasone phosphate+betamethasone acetate group, n=12); or (3) 2 maternal intramuscular injections of 0.125 mg/kg betamethasone acetate administered at 24-hour dosing intervals (the betamethasone acetate group, n=11). The fetuses were surgically delivered 48 hours after treatment initiation and ventilated for 30 minutes to determine functional lung maturation. The fetuses were euthanized after ventilation, and the lungs were collected for analysis using quantitative polymerase chain reaction and Western blot assays. Fetal plasma adrenocorticotropic hormone levels were measured in the cord blood samples taken at delivery.

RESULTS

Preterm lambs were defined as either antenatal corticosteroid treatment responders or nonresponders using an arbitrary cutoff, being a PaCO₂ level at 30 minutes of ventilation being more extreme than 2 standard deviations from the mean value of the normally distributed saline control group values. Compared with the animals in the saline control group, the animals in the antenatal corticosteroid treatment groups showed significantly improved lung physiological responses (blood gas and ventilation data) and had a biochemical signature (messenger RNA and surfactant protein assays) consistent with functional maturation. However, the betamethasone acetate group had a significantly higher treatment response rate than the betamethasone phosphate+betamethasone acetate group. These physiological results were strongly correlated to the amount of surfactant protein A. Birthweight was lower in the betamethasone phosphate+betamethasone acetate group and the fetal hypothalamic-pituitary-adrenal axis was suppressed to a greater extent in the betamethasone phosphate+betamethasone acetate group.

CONCLUSION

Low-dosage antenatal corticosteroid therapy solely employing betamethasone acetate was sufficient for fetal lung maturation. The elevated maternal-fetal betamethasone concentrations associated with the coadministration of betamethasone phosphate did not in addition improve lung maturation but were associated with greater fetal hypothalamic-pituitary-adrenal axis suppression, a lower antenatal corticosteroid treatment response rate, and lower birthweight-outcomes not desirable in a clinical setting. These data warranted a clinical investigation of sustained low-dosage antenatal corticosteroid treatments that avoid high maternal-fetal betamethasone exposures.

Time interval from late preterm antenatal corticosteroid administration to delivery and the impact on neonatal outcomes

BACKGROUND

Although administration of antenatal corticosteroids has been shown to decrease neonatal respiratory morbidity when given to women at risk for late preterm birth, the time interval from antenatal corticosteroid administration to delivery that is associated with the greatest neonatal benefit remains unknown.

OBJECTIVE

This study aimed to evaluate whether the time interval from administration of late preterm antenatal corticosteroids to delivery is associated with a change in the likelihood of transient tachypnea of the newborn, respiratory distress syndrome, and hypoglycemia.

STUDY DESIGN

This was a retrospective cohort study of all singleton neonates who were exposed to 1 or 2 doses of antenatal corticosteroids in the late preterm period (34+0 to 36+6 weeks' gestation) within a large healthcare system between November 2017 and March 2020. Neonates exposed to antenatal corticosteroids before 34 weeks' gestation and those with major fetal structural malformations and chromosomal disorders were excluded. Cases were stratified into the following groups based on the time interval from the first dose of antenatal corticosteroid administration to delivery: <2 days, 2 to 7 days, and >7 days. The primary outcome of transient tachypnea of the newborn was compared among the 3 groups. Secondary outcomes included respiratory distress syndrome and hypoglycemia. A multivariable logistic regression was performed to evaluate the association between the time interval and neonatal outcomes while adjusting for potential confounders. For each outcome, delivery within 2 to 7 days from the first dose of betamethasone administration was defined as the reference group. Data were presented as adjusted odds ratios with 95% confidence intervals, and statistical significance was defined as P < .05.

RESULTS

The study cohort comprised 1248 neonates. Of those, 649 (52%) were exposed to 1 dose of antenatal corticosteroids. There were statistically significant differences in the maternal characteristics such as nulliparity, pregnancies complicated by hypertensive disorders and fetal growth restriction, gestational age at antenatal corticosteroid administration, gestational age at delivery, and mode of delivery among the 3 groups. There was a significantly increased risk for transient tachypnea of the newborn (adjusted odds ratio, 4.81; 95% confidence interval, 1.72-12.92) and respiratory distress syndrome (adjusted odds ratio, 9.86; 95% confidence interval, 1.15-84.24) associated with delivery <2 days of antenatal corticosteroid administration. The risk for hypoglycemia was highest in the delivery <2 days group (adjusted odds ratio, 3.44; 95% confidence interval, 2.10-5.63) and decreased as the time interval from antenatal corticosteroid administration to delivery increased (adjusted odds ratio, 0.32; 95% confidence interval, 0.20-0.51 for delivery >7 days).

CONCLUSION

Adverse neonatal outcomes such as transient tachypnea of the newborn, respiratory distress syndrome, and hypoglycemia are more common when late preterm birth occurs <2 days after antenatal corticosteroid administration when compared with birth 2 to 7 days after administration. In addition, delivery >7 days after antenatal corticosteroid administration is associated with a decreased risk for hypoglycemia. Understanding the impact of antenatal corticosteroid timing on neonatal outcomes is essential in caring for patients at risk for late preterm birth.

Chapter for antenatal steroids - Treatment drift for a potent therapy with unknown long-term safety seminars in fetal and neonatal medicine

This chapter on therapeutic drift with antenatal steroids will make the case that this pilar of treatment to improve the outcomes of preterm infants, despite multiple Randomized Control Trials (RCTs) and meta-analysis, has multiple gaps in solid clinical data to support any expanded use of Antenatal Corticosteroids (ACS). A basic problem is that agents used for ACS have never been evaluated to minimize fetal exposures. Based on the premise that all drug exposure to the fetus should be minimized and only used when necessary, ACS is a potent developmental modulator that has never been evaluated to minimize the dose and duration of fetal exposure. The use of ACS is expanding to late preterm infants where the benefit is modest, to elective C-sections, and periviable fetuses, with minimal RCT data of long-term benefit. Relevant animal experiments demonstrate that much lower doses will induce lung maturation in sheep and primates. Another area of drift in the use of ACS is based on the assumption that the old RCT data accurately predict the magnitude of benefit when ACS is used today with entirely different OB and neonatal care strategies to improve outcomes. We do not have data that demonstrate the effectiveness of ACS in very low resource environments, where most of the preterm mortality occurs. The final concern is the risk of ACS to the infant and child. Short-term risks are minimal but dysmaturation effects of ACS on multiple organ systems (lung, heart, brain, and kidney) may result in disease presentation in later life.

Antenatal corticosteroids: a reappraisal of the drug formulation and dose

We review the history of antenatal corticosteroid therapy (ACS) and present recent experimental data to demonstrate that this, one of the pillars of perinatal care, has been inadequately evaluated to minimize fetal exposure to these powerful medications. There have been concerns since 1972 that fetal exposures to ACS convey risk. However, this developmental modulator, with its multiple widespread biologic effects, has not been evaluated for drug choice, dose, or duration of treatment, despite over 30 randomized trials. The treatment used in the United States is two intramuscular doses of a mixture of 6 mg betamethasone phosphate (Beta P) and 6 mg betamethasone acetate (Beta Ac). To optimize outcomes with ACS, the goal should be to minimize fetal drug exposure. We have determined that the minimum exposure needed for fetal lung maturation in sheep, monkeys, and humans (based on published cord blood corticosteroid concentrations) is about 1 ng/ml for a 48-h continuous exposure, far lower than the concentration reached by the current dosing. Because the slowly released Beta Ac results in prolonged fetal exposure, a drug containing Beta Ac is not ideal for ACS use. IMPACT: Using sheep and monkey models, we have defined the minimum corticosteroid exposure for a fetal lung maturation. These results should generate new clinical trials of antenatal corticosteroids (ACS) at much lower fetal exposures to ACS, possibly given orally, with fewer risks for the fetus.

Variability in the efficacy of a standardized antenatal steroid treatment was independent of maternal or fetal plasma drug levels: evidence from a sheep model of pregnancy

BACKGROUND

Administration of antenatal steroids is standard of care for women assessed to be at imminent risk of preterm delivery. There is a marked variation in antenatal steroid dosing strategy, selection for treatment criteria, and agent choice worldwide. This, combined with very limited optimization of antenatal steroid use per se, means that treatment efficacy is highly variable, and the rate of respiratory distress syndrome is decreased to perhaps as low as 40%. In some cases, antenatal steroid use is associated with limited benefit and potential harm.

OBJECTIVE

We hypothesized that individual differences in maternofetal steroid exposure would contribute to observed variability in antenatal steroid treatment efficacy. Using a chronically catheterized sheep model of pregnancy, we aimed to explore the relationship between maternofetal steroid exposure and antenatal steroid treatment efficacy as determined by functional lung maturation in preterm lambs undergoing ventilation.

STUDY DESIGN

Ewes carrying a single fetus underwent surgery to catheterize a fetal and maternal jugular vein at 119 days' gestation. Animals recovered for 24 hours before being randomized to either (1) a single maternal intramuscular injection of 2 mL saline (negative control group, n=10) or (2) a single maternal intramuscular injection of 0.25 mg/kg betamethasone phosphate plus acetate (antenatal steroid group, n=20). Serial maternal and fetal plasma samples were collected from each animal after 48 hours before fetuses were delivered and ventilated for 30 minutes. Total and free plasma betamethasone concentration was measured by mass spectrometry. Fetal lung tissue was collected for analysis using quantitative polymerase chain reaction.

RESULTS

One animal from the control group and one animal from the antenatal steroid group did not complete their treatment protocol and were removed from analyses. Animals in the antenatal steroid group were divided into a responder subgroup (n=12/19) and a nonresponder subgroup (n=7/19) using a cutoff of partial pressure of arterial CO₂ at 30-minute ventilation within 2 standard deviations of the mean value from saline-treated negative control group animals. Although antenatal steroid improved fetal lung maturation in the undivided antenatal steroid group and in the responder subgroup both physiologically (blood gas- and ventilation-related data) and biochemically (messenger ribonucleic acid expression related to fetal lung maturation), these values did not improve relative to saline-treated control group animals in the antenatal steroid nonresponder subgroup. No differences in betamethasone distribution, clearance, or protein binding were identified between the antenatal steroid responder and nonresponder subgroups.

CONCLUSION

This study correlated individual maternofetal steroid exposures with preterm lung maturation as determined by pulmonary ventilation. Herein, approximately 40% of preterm lambs exposed to antenatal steroids had lung maturation that was not significantly different to saline-treated control group animals. These nonresponsive animals received maternal and fetal betamethasone exposures identical to animals that had a significant improvement in functional lung maturation. These data suggest that the efficacy of antenatal steroid therapy is not solely determined by maternofetal drug levels and that individual fetal or maternal factors may play a role in determining treatment outcomes in response to glucocorticoid signaling.

Maternal Betamethasone for Prevention of Respiratory Distress Syndrome in Neonates: Population Pharmacokinetic and Pharmacodynamic Approach

Despite antenatal corticosteroids therapy, respiratory distress syndrome (RDS) is still a leading cause of neonatal morbidity and mortality in premature newborns. To date, the relationship between in utero fetal drug exposure and occurrence of RDS remains poorly evaluated. This study aims to describe the pharmacokinetics of betamethasone in pregnant women and to evaluate the transplacental drug transfer and administration scheme for the prevention of RDS. Pregnant women > 27 weeks' gestation and who received at least a single dose of betamethasone for prevention of RDS were enrolled. Maternal, cord blood, and amniotic fluid betamethasone time-courses were analyzed using the Monolix software. A total of 220 maternal blood, 56 cord blood, and 26 amniotic fluid samples were described by a two-compartment model with two effect compartments linked by rate transfer constants. Apparent clearances and volumes of distribution parameters were allometrically scaled for a 70 kg third trimester pregnant woman. The impact of a twin pregnancy was found to increase maternal clearance by 28%. Using a fetal-to-mother exposure ratio, the median (95% confidence interval (CI)) transplacental transfer of betamethasone was estimated to 35% (95% CI 0.11-0.67). After adjustment for gestational age and twin pregnancy, RDS was found to be associated to the time spent in utero below quantifiable concentrations (i.e., < 1 ng/mL): odds ratio of 1.10 (95% CI 1.01-1.19) per day increase (P < 0.05). Trying to take into account both efficacy and safety, we simulated different dosing schemes in order to maintain a maximum of fetuses above 1 ng/mL without exceeding the total standard dose.

Glucocorticoid regulates mesenchymal cell differentiation required for perinatal lung morphogenesis and function

While antenatal glucocorticoids are widely used to enhance lung function in preterm infants, cellular and molecular mechanisms by which glucocorticoid receptor (GR) signaling influences lung maturation remain poorly understood. Deletion of the glucocorticoid receptor gene (Nr3c1) from fetal pulmonary mesenchymal cells phenocopied defects caused by global Nr3c1 deletion, while lung epithelial- or endothelial-specific Nr3c1 deletion did not impair lung function at birth. We integrated genome-wide gene expression profiling, ATAC-seq, and single cell RNA-seq data in mice in which GR was deleted or activated to identify the cellular and molecular mechanisms by which glucocorticoids control prenatal lung maturation. GR enhanced differentiation of a newly defined proliferative mesenchymal progenitor cell (PMP) into matrix fibroblasts (MFBs), in part by directly activating extracellular matrix-associated target genes, including Fn1, Col16a4, and Eln and by modulating VEGF, JAK-STAT, and WNT signaling. Loss of mesenchymal GR signaling blocked fibroblast progenitor differentiation into mature MFBs, which in turn increased proliferation of SOX9+ alveolar epithelial progenitor cells and inhibited differentiation of mature alveolar type II (AT₂) and AT₁ cells. GR signaling controls genes required for differentiation of a subset of proliferative mesenchymal progenitors into matrix fibroblasts, in turn, regulating signals controlling AT₂/AT₁ progenitor cell proliferation and differentiation and identifying cells and processes by which glucocorticoid signaling regulates fetal lung maturation.

ERS International Congress, Madrid, 2019: highlights from the Basic and Translational Science Assembly

In this review, the Basic and Translational Sciences Assembly of the European Respiratory Society (ERS) provides an overview of the 2019 ERS International Congress highlights. In particular, we discuss how the novel and very promising technology of single cell sequencing has led to the development of a comprehensive map of the human lung, the lung cell atlas, including the discovery of novel cell types and new insights into cellular trajectories in lung health and disease. Further, we summarise recent insights in the field of respiratory infections, which can aid in a better understanding of the molecular mechanisms underlying these infections in order to develop novel vaccines and improved treatment options. Novel concepts delineating the early origins of lung disease are focused on the effects of pre- and post-natal exposures on neonatal lung development and long-term lung health. Moreover, we discuss how these early life exposures can affect the lung microbiome and respiratory infections. In addition, the importance of metabolomics and mitochondrial function analysis to subphenotype chronic lung disease patients according to their metabolic program is described. Finally, basic and translational respiratory science is rapidly moving forward and this will be beneficial for an advanced molecular understanding of the mechanisms underlying a variety of lung diseases. In the long-term this will aid in the development of novel therapeutic targeting strategies in the field of respiratory medicine.

Highlights of basic and translational science presented at #ERSCongress 2019 summarising latest research on the lung cell atlas, lung infections, early origins of lung disease and the importance of metabolic alterations in the lunghttp://bit.ly/2UbdBs4

Pharmacokinetics and Pharmacodynamics of Intramuscular and Oral Betamethasone and Dexamethasone in Reproductive Age Women in India

High-dose betamethasone and dexamethasone are standard of care treatments for women at risk of preterm delivery to improve neonatal respiratory and mortality outcomes. The dose in current use has never been evaluated to minimize exposures while assuring efficacy. We report the pharmacokinetics and pharmacodynamics (PDs) of oral and intramuscular treatments with single 6 mg doses of dexamethasone phosphate, betamethasone phosphate, or a 1:1 mixture of betamethasone phosphate and betamethasone acetate in reproductive age South Asian women. Intramuscular or oral betamethasone has a terminal half-life of 11 hours, about twice as long as the 5.5 hours for oral and intramuscular dexamethasone. The 1:1 mixture of betamethasone phosphate and betamethasone acetate shows an immediate release of betamethasone followed by a slow release where plasma betamethasone can be measured out to 14 days after the single dose administration, likely from a depo formed at the injection site by the acetate. PD responses were: increased glucose, suppressed cortisol, increased neutrophils, and suppressed basophils, CD3CD4 and CD3CD8 lymphocytes. PD responses were comparable for betamethasone and dexamethasone, but with longer times to return to baseline for betamethasone. The 1:1 mixture of betamethasone phosphate and betamethasone acetate caused much longer adrenal suppression because of the slow release. These results will guide the development of better treatment strategies to minimize fetal and maternal drug exposures for women at risk of preterm delivery.