Secular Trends in Patent Ductus Arteriosus Management in Infants Born Preterm in the National Institute of Child Health and Human Development Neonatal Research Network.

We evaluated changes in patent ductus arteriosus (PDA) diagnosis and treatment from 2012 through 2021 in a network of US academic hospitals. PDA treatment decreased among infants born at 26-28 weeks but not among infants born at 22-25 weeks. Rates of indomethacin use and PDA ligation decreased while acetaminophen use and transcatheter PDA closure increased.

Practical approaches for supporting informed consent in neonatal clinical trials.

The survival and health of preterm and critically ill infants have markedly improved over the past 50 years, supported by well-conducted neonatal research. However, newborn research is difficult to undertake for many reasons, and obtaining informed consent for research in this population presents several unique ethical and logistical challenges. In this article, we explore methods to facilitate the consent process, including the role of checklists to support meaningful informed consent for neonatal clinical trials. CONCLUSION: The authors provide practical guidance on the design and implementation of an effective consent checklist tailored for use in neonatal clinical research.

Generalizability of the Necrotizing Enterocolitis Surgery Trial to the Target Population of Eligible Infants.

OBJECTIVE: The objective of this study was to evaluate whether infants randomized in the Eunice Kennedy Shriver National Institute of Child Health and Human Development Neonatal Research Network Necrotizing Enterocolitis Surgery Trial differed from eligible infants and whether differences affected the generalizability of trial results. STUDY DESIGN: Secondary analysis of infants enrolled in Necrotizing Enterocolitis Surgery Trial (born 2010-2017, with follow-up through 2019) at 20 US academic medical centers and an observational data set of eligible infants through 2013. Infants born ≤1000 g and diagnosed with necrotizing enterocolitis or spontaneous intestinal perforation requiring surgical intervention at ≤8 weeks were eligible. The target population included trial-eligible infants (randomized and nonrandomized) born during the first half of the study with available detailed preoperative data. Using model-based weighting methods, we estimated the effect of initial laparotomy vs peritoneal drain had the target population been randomized. RESULTS: The trial included 308 randomized infants. The target population included 382 (156 randomized and 226 eligible, non-randomized) infants. Compared with the target population, fewer randomized infants had necrotizing enterocolitis (31% vs 47%) or died before discharge (27% vs 41%). However, incidence of the primary composite outcome, death or neurodevelopmental impairment, was similar (69% vs 72%). Effect estimates for initial laparotomy vs drain weighted to the target population were largely unchanged from the original trial after accounting for preoperative diagnosis of necrotizing enterocolitis (adjusted relative risk [95% CI]: 0.85 [0.71-1.03] in target population vs 0.81 [0.64-1.04] in trial) or spontaneous intestinal perforation (1.02 [0.79-1.30] vs 1.11 [0.95-1.31]). CONCLUSION: Despite differences between randomized and eligible infants, estimated treatment effects in the trial and target population were similar, supporting the generalizability of trial results. TRIAL REGISTRATION: ClinicalTrials.gov ID: NCT01029353.

Evaluation of heterogeneity in effect of therapeutic hypothermia by sex among infants with neonatal encephalopathy.

BACKGROUND: Our objective was to examine heterogeneity in the effect of therapeutic hypothermia by sex in infants with moderate or severe neonatal encephalopathy. METHODS: We conducted a post hoc analysis of the Induced Hypothermia trial, which included infants born at gestational ages ≥36 weeks, admitted at ≤6 postnatal hours with evidence of severe acidosis or perinatal complications and moderate or severe neonatal encephalopathy. Multivariate modified Poisson regression models were used to compare the treatment effect of whole-body hypothermia versus control, with an evaluation of interaction by sex, on the primary outcome of death or moderate or severe disability at 18-22 months of corrected age. RESULTS: A total of 101 infants (51 male, 50 female) were randomly assigned to hypothermia treatment and 104 infants (64 male, 40 female) to control. The primary outcome occurred in 45% of the hypothermia group and 63% of the control group (RR 0.73; 95% CI 0.56, 0.94). There was no significant difference (interaction P = 0.50) in the treatment effect of hypothermia on the primary outcome between females (RR 0.79; 95% CI 0.54, 1.17) compared to males (RR 0.63; 95% CI 0.44, 0.91). CONCLUSION: We found no evidence that sex influences the treatment effect of hypothermia in infants with moderate or severe neonatal encephalopathy. IMPACT: Preclinical evidence suggests a differential effect in response to cooling treatment of hypoxic-ischemic injury between males and females. We found no evidence of heterogeneity in the treatment effect of whole-body hypothermia by sex in this post hoc subgroup analysis of infants with moderate or severe neonatal encephalopathy from the National Institute of Child Health and Human Development Neonatal Research Network Induced Hypothermia trial.

Effect of reduced versus usual lipid emulsion dosing on bilirubin neurotoxicity and neurodevelopmental impairment in extremely preterm infants: study protocol for a randomized controlled trial.

BACKGROUND: Bilirubin neurotoxicity (BN) occurs in premature infants at lower total serum bilirubin levels than term infants and causes neurodevelopmental impairment. Usual dose lipid infusions in preterm infants may increase free fatty acids sufficiently to cause bilirubin displacement from albumin, increasing passage of unbound bilirubin (UB) into the brain leading to BN and neurodevelopmental impairment not reliably identifiable in infancy. These risks may be influenced by whether cycled or continuous phototherapy is used to control bilirubin levels. OBJECTIVE: To assess differences in wave V latency measured by brainstem auditory evoked responses (BAER) at 34-36 weeks gestational age in infants born ≤ 750 g or < 27 weeks' gestational age randomized to receive usual or reduced dose lipid emulsion (half of the usual dose) irrespective of whether cycled or continuous phototherapy is administered. METHODS: Pilot factorial randomized controlled trial (RCT) of lipid dosing (usual and reduced) with treatment groups balanced between cycled or continuous phototherapy assignment. Eligible infants are born at ≤ 750 g or < 27 weeks' gestational age enrolled in the NICHD Neonatal Research Network RCT of cycled or continuous phototherapy. Infants will randomize 1:1 to reduced or usual dose lipid assignment during the first 2 weeks after birth and stratified by phototherapy assignment. Free fatty acids and UB will be measured daily using a novel probe. BAER testing will be performed at 34-36 weeks postmenstrual age or prior to discharge. Blinded neurodevelopmental assessments will be performed at 22-26 months. Intention-to-treat analyses will be performed with generalized linear mixed models with lipid dose and phototherapy assignments as random effects covariates, and assessment for interactions. Bayesian analyses will be performed as a secondary analysis. DISCUSSION: Pragmatic trials are needed to evaluate whether lipid emulsion dosing modifies the effect of phototherapy on BN. This factorial design presents a unique opportunity to evaluate both therapies and their interaction. This study aims to address basic controversial questions about the relationships between lipid administration, free fatty acids, UB, and BN. Findings suggesting a reduced lipid dose can diminish the risk of BN would support the need for a large multicenter RCT of reduced versus usual lipid dosing. TRIAL REGISTRATION: Clinical Trials.gov, NCT04584983, Registered 14 October 2020, https://clinicaltrials.gov/ct2/show/NCT04584983 Protocol version: Version 3.2 (10/5/2022).

Active Treatment of Infants Born at 22-25 Weeks of Gestation in California, 2011-2018.

OBJECTIVE: To determine the rate and trend of active treatment in a population-based cohort of infants born at 22-25 weeks of gestation and to examine factors associated with active treatment. STUDY DESIGN: This observational study evaluated 8247 infants born at 22-25 weeks of gestation at hospitals in the California Perinatal Quality Care Collaborative between 2011 and 2018. Multivariable logistic regression was used to relate maternal demographic and prenatal factors, fetal characteristics, and hospital level of care to the primary outcome of active treatment. RESULTS: Active treatment was provided to 6657 infants. The rate at 22 weeks was 19.4% and increased with each advancing week, and was significantly higher for infants born between days 4 and 6 at 22 or 23 weeks of gestation compared with those born between days 0 and 3 (26.2% and 78.3%, respectively, vs 14.1% and 65.9%, respectively; P < .001). The rate of active treatment at 23 weeks increased from 2011 to 2018 (from 64.9% to 83.4%; P < .0001) but did not change significantly at 22 weeks. Factors associated with increased odds of active treatment included maternal Hispanic ethnicity and Black race, preterm premature rupture of membranes, obstetrical bleeding, antenatal steroids, and cesarean delivery. Factors associated with decreased odds included lower gestational age and small for gestational age birth weight. CONCLUSIONS: In California, active treatment rates at 23 weeks of gestation increased between 2011 and 2018, but rates at 22 weeks did not. At 22 and 23 weeks, rates increased during the latter part of the week. Several maternal and infant factors were associated with the likelihood of active treatment.

Potential missed opportunities for antenatal corticosteroid exposure and outcomes among periviable births: observational cohort study.

OBJECTIVE: Test the hypothesis potential missed opportunities for antenatal corticosteroids increase as gestational age decreases and are associated with adverse outcomes. DESIGN: Observational cohort study. SETTING: 24 US centers in the Neonatal Research Network. POPULATION: Actively treated infants 22-25 weeks' gestation and birth weight 401-1000 grams, without major birth defects, born 2006-2018. METHODS: Potential missed opportunity was defined as no antenatal corticosteroids but did have prenatal antibiotics, and/or magnesium sulfate, and/or prolonged rupture of membranes. Poisson regression models adjusted for baseline characteristics. MAIN OUTCOME MEASURES: Antenatal corticosteroid exposure, mortality, and severe intracranial hemorrhage or periventricular leukomalacia. RESULTS: 6966 (87.5%) were exposed to antenatal corticosteroids, 454 (5.7%) had no exposure but potential missed opportunities for antenatal corticosteroid exposure, and 537 (6.7%) had no exposure and no evidence of potential missed opportunities. Compared with infants born at 25 weeks, potential missed opportunities for antenatal corticosteroid exposure were more likely at 22 weeks (adjusted relative risk (aRR) [95% CI] 11.06 [7.52-16.27]) and 23 weeks (3.24 [2.44-4.29]) but did not differ at 24 weeks (1.08 [0.82-1.42]). Potential missed opportunities for antenatal corticosteroids decreased over time at 22-23 weeks' gestation. Antenatal corticosteroid exposed infants had lower risk of death (31.0% vs 54.8%; 0.77 [0.70-0.84]) and survivors had lower risk of severe brain injury (25.0% v 44.5%; 0.64 [0.55-0.73]) compared with infants with potential missed opportunities. CONCLUSION: Potential missed opportunities for antenatal corticosteroid exposure increased with decreasing gestational age and were associated with higher rates of death and severe brain injury among actively treated periviable births.

Mortality, In-Hospital Morbidity, Care Practices, and 2-Year Outcomes for Extremely Preterm Infants in the US, 2013-2018.

IMPORTANCE: Despite improvement during recent decades, extremely preterm infants continue to contribute disproportionately to neonatal mortality and childhood morbidity. OBJECTIVE: To review survival, in-hospital morbidities, care practices, and neurodevelopmental and functional outcomes at 22-26 months' corrected age for extremely preterm infants. DESIGN, SETTING, AND PARTICIPANTS: Prospective registry for extremely preterm infants born at 19 US academic centers that are part of the Eunice Kennedy Shriver National Institute of Child Health and Human Development Neonatal Research Network. The study included 10 877 infants born at 22-28 weeks' gestational age between January 1, 2013, and December 31, 2018, including 2566 infants born before 27 weeks between January 1, 2013, and December 31, 2016, who completed follow-up assessments at 22-26 months' corrected age. The last assessment was completed on August 13, 2019. Outcomes were compared with a similar cohort of infants born in 2008-2012 adjusting for gestational age. EXPOSURES: Extremely preterm birth. MAIN OUTCOMES AND MEASURES: Survival and 12 in-hospital morbidities were assessed, including necrotizing enterocolitis, infection, intracranial hemorrhage, retinopathy of prematurity, and bronchopulmonary dysplasia. Infants were assessed at 22-26 months' corrected age for 12 health and functional outcomes, including neurodevelopment, cerebral palsy, vision, hearing, rehospitalizations, and need for assistive devices. RESULTS: The 10 877 infants were 49.0% female and 51.0% male; 78.3% (8495/10848) survived to discharge, an increase from 76.0% in 2008-2012 (adjusted difference, 2.0%; 95% CI, 1.0%-2.9%). Survival to discharge was 10.9% (60/549) for live-born infants at 22 weeks and 94.0% (2267/2412) at 28 weeks. Survival among actively treated infants was 30.0% (60/200) at 22 weeks and 55.8% (535/958) at 23 weeks. All in-hospital morbidities were more likely among infants born at earlier gestational ages. Overall, 8.9% (890/9956) of infants had necrotizing enterocolitis, 2.4% (238/9957) had early-onset infection, 19.9% (1911/9610) had late-onset infection, 14.3% (1386/9705) had severe intracranial hemorrhage, 12.8% (1099/8585) had severe retinopathy of prematurity, and 8.0% (666/8305) had severe bronchopulmonary dysplasia. Among 2930 surviving infants with gestational ages of 22-26 weeks eligible for follow-up, 2566 (87.6%) were examined. By 2-year follow-up, 8.4% (214/2555) of children had moderate to severe cerebral palsy, 1.5% (38/2555) had bilateral blindness, 2.5% (64/2527) required hearing aids or cochlear implants, 49.9% (1277/2561) had been rehospitalized, and 15.4% (393/2560) required mobility aids or other supportive devices. Among 2458 fully evaluated infants, 48.7% (1198/2458) had no or mild neurodevelopmental impairment at follow-up, 29.3% (709/2419) had moderate neurodevelopmental impairment, and 21.2% (512/2419) had severe neurodevelopmental impairment. CONCLUSIONS AND RELEVANCE: Among extremely preterm infants born in 2013-2018 and treated at 19 US academic medical centers, 78.3% survived to discharge, a significantly higher rate than for infants born in 2008-2012. Among infants born at less than 27 weeks' gestational age, rehospitalization and neurodevelopmental impairment were common at 2 years of age.

Should Vitamin A Injections to Prevent Bronchopulmonary Dysplasia or Death Be Reserved for High-Risk Infants? Reanalysis of the National Institute of Child Health and Human Development Neonatal Research Network Randomized Trial.

OBJECTIVE: To determine whether infants at higher risk of bronchopulmonary dysplasia (BPD) or death benefit more from vitamin A therapy than those at lower risk. STUDY DESIGN: We conducted a post hoc reanalysis of a landmark phase III randomized controlled trial conducted from January 1996 to July 1997 at 14 university-affiliated neonatal intensive care units in the US. Data analysis was performed from October 2019 to October 2020. Infants born weighing 401-1000 g and receiving respiratory support at 24 hours of age were assigned to intramuscular vitamin A 5000 IU or sham procedure 3 times weekly for 4 weeks. The primary outcome was BPD, defined as use of supplemental oxygen, or death at 36 weeks postmenstrual age. An externally validated model for predicting BPD or death was used to estimate the risk of these outcomes for each infant. RESULTS: As previously reported, 222 of 405 infants (54.8%) assigned vitamin A therapy and 248 of 402 infants (61.7%) in the control group developed BPD or died (relative risk [RR], 0.89 [95% CI, 0.80-0.99]; risk difference [RD], -6.9% [95% CI, -13.0 to -0.7]). The predicted individual risks of BPD or death ranged from 7.1% to 98.6% (median, 61.5%; mean, 60.9%). The effect of vitamin A therapy on BPD or death depended on infants' risk of the primary outcome (P = .03 for interaction): for example, a RR of 0.73 (RD, -14.5%) for infants with a 25% predicted risk and a RR of 0.96 (RD, -1.0%) for infants with a 75% risk. There was no difference in the decrease in vitamin A deficiency across risk groups. CONCLUSIONS: Contrary to expectations, the effect of vitamin A therapy on BPD or death was greater for lower risk than higher risk infants. TRIAL REGISTRATION: ClinicalTrials.gov NCT01203488.

Eligibility Criteria and Representativeness of Randomized Clinical Trials That Include Infants Born Extremely Premature: A Systematic Review.

OBJECTIVE: To assess the eligibility criteria and trial characteristics among contemporary (2010-2019) randomized clinical trials (RCTs) that included infants born extremely preterm (<28 weeks of gestation) and to evaluate whether eligibility criteria result in underrepresentation of high-risk subgroups (eg, infants born at <24 weeks of gestation). STUDY DESIGN: PubMed and Scopus were searched January 1, 2010, to December 31, 2019, with no language restrictions. RCTs with mean or median gestational ages at birth of <28 weeks of gestation were included. The study followed the PRISMA guidelines; outcomes were registered prospectively. Data extraction was performed independently by multiple observers. Study quality was evaluated using a modified Jadad scale. RESULTS: Among RCTs (n = 201), 32 552 infants were included. Study participant characteristics, interventions, and outcomes were highly variable. A total of 1603 eligibility criteria were identified; rationales were provided for 18.8% (n = 301) of criteria. Fifty-five RCTs (27.4%) included infants <24 weeks of gestation; 454 (1.4%) infants were identified as <24 weeks of gestation. CONCLUSIONS: The present study identifies sources of variability across RCTs that included infants born extremely preterm and reinforces the critical need for consistent and transparent policies governing eligibility criteria.

Survival and Neurodevelopmental Outcomes among Periviable Infants.

BACKGROUND: Data reported during the past 5 years indicate that rates of survival have increased among infants born at the borderline of viability, but less is known about how increased rates of survival among these infants relate to early childhood neurodevelopmental outcomes. METHODS: We compared survival and neurodevelopmental outcomes among infants born at 22 to 24 weeks of gestation, as assessed at 18 to 22 months of corrected age, across three consecutive birth-year epochs (2000-2003 [epoch 1], 2004-2007 [epoch 2], and 2008-2011 [epoch 3]). The infants were born at 11 centers that participated in the National Institute of Child Health and Human Development Neonatal Research Network. The primary outcome measure was a three-level outcome - survival without neurodevelopmental impairment, survival with neurodevelopmental impairment, or death. After accounting for differences in infant characteristics, including birth center, we used multinomial generalized logit models to compare the relative risk of survival without neurodevelopmental impairment, survival with neurodevelopmental impairment, and death. RESULTS: Data on the primary outcome were available for 4274 of 4458 infants (96%) born at the 11 centers. The percentage of infants who survived increased from 30% (424 of 1391 infants) in epoch 1 to 36% (487 of 1348 infants) in epoch 3 (P<0.001). The percentage of infants who survived without neurodevelopmental impairment increased from 16% (217 of 1391) in epoch 1 to 20% (276 of 1348) in epoch 3 (P=0.001), whereas the percentage of infants who survived with neurodevelopmental impairment did not change significantly (15% [207 of 1391] in epoch 1 and 16% [211 of 1348] in epoch 3, P=0.29). After adjustment for changes in the baseline characteristics of the infants over time, both the rate of survival with neurodevelopmental impairment (as compared with death) and the rate of survival without neurodevelopmental impairment (as compared with death) increased over time (adjusted relative risks, 1.27 [95% confidence interval {CI}, 1.01 to 1.59] and 1.59 [95% CI, 1.28 to 1.99], respectively). CONCLUSIONS: The rate of survival without neurodevelopmental impairment increased between 2000 and 2011 in this large cohort of periviable infants. (Funded by the National Institutes of Health and others; ClinicalTrials.gov numbers, NCT00063063 and NCT00009633 .).

Behavior Profiles at 2 Years for Children Born Extremely Preterm with Bronchopulmonary Dysplasia.

OBJECTIVE: To characterize behavior of 2-year-old children based on the severity of bronchopulmonary dysplasia (BPD). STUDY DESIGN: We studied children born at 22-26 weeks of gestation and assessed at 22-26 months of corrected age with the Child Behavior Checklist (CBCL). BPD was classified by the level of respiratory support at 36 weeks of postmenstrual age. CBCL syndrome scales were the primary outcomes. The relationship between BPD grade and behavior was evaluated, adjusting for perinatal confounders. Mediation analysis was performed to evaluate whether cognitive, language, or motor skills mediated the effect of BPD grade on behavior. RESULTS: Of 2310 children, 1208 (52%) had no BPD, 806 (35%) had grade 1 BPD, 177 (8%) had grade 2 BPD, and 119 (5%) had grade 3 BPD. Withdrawn behavior (P < .001) and pervasive developmental problems (P < .001) increased with worsening BPD grade. Sleep problems (P = .008) and aggressive behavior (P = .023) decreased with worsening BPD grade. Children with grade 3 BPD scored 2 points worse for withdrawn behavior and pervasive developmental problems and 2 points better for externalizing problems, sleep problems, and aggressive behavior than children without BPD. Cognitive, language, and motor skills mediated the effect of BPD grade on the attention problems, emotionally reactive, somatic complaints, and withdrawn CBCL syndrome scales (P values < .05). CONCLUSIONS: BPD grade was associated with increased risk of withdrawn behavior and pervasive developmental problems but with decreased risk of sleep problems and aggressive behavior. The relationship between BPD and behavior is complex. Cognitive, language, and motor skills mediate the effects of BPD grade on some problem behaviors.

Discordance in Antenatal Corticosteroid Use and Resuscitation Following Extremely Preterm Birth.

OBJECTIVE: To describe discordance in antenatal corticosteroid use and resuscitation following extremely preterm birth and its relationship with infant survival and neurodevelopment. STUDY DESIGN: A multicenter cohort study of 4858 infants 22-26 weeks of gestation born 2006-2011 at 24 US hospitals participating in the Eunice Kennedy Shriver National Institute of Child Health and Human Development Neonatal Research Network, with follow-up through 2013. Survival and neurodevelopmental outcomes were available at 18-22 months of corrected age for 4576 (94.2%) infants. We described antenatal interventions, resuscitation, and infant outcomes. We modeled the effect on infant outcomes of each hospital increasing antenatal corticosteroid exposure for resuscitated infants born at 22-24 weeks of gestation to rates observed at 25-26 weeks of gestation. RESULTS: Discordant antenatal corticosteroid use and resuscitation, where one and not the other occurred, were more frequent for births at 22 and 23 but not 24 weeks (rate ratio [95% CI] at 22 weeks: 1.7 [1.3-2.2]; 23 weeks: 2.6 [2.2-3.2]; 24 weeks: 1.0 [0.8-1.2]) when compared with 25-26 weeks. Among infants resuscitated at 23 weeks, adjusting each hospital's rate of antenatal corticosteroid use to the average at 25-26 weeks (89.2%) was projected to increase infant survival by 7.1% (95% CI 5.4-8.8%) and survival without severe impairment by 6.4% (95% CI 4.7-8.1%). No significant change in outcomes was projected for infants resuscitated at 22 weeks, where few (n = 22) resuscitated infants received antenatal corticosteroids. CONCLUSIONS: Infants born at 23 weeks were more frequently resuscitated without antenatal corticosteroids than other extremely preterm infants. When resuscitation is intended, consistent provision of antenatal corticosteroids may increase infant survival and survival without impairment. TRIAL REGISTRATION: ClinicalTrials.govNCT00063063 (Generic Database) and NCT00009633 (Follow-Up Study).

Between-hospital variation in treatment and outcomes in extremely preterm infants.

BACKGROUND: Between-hospital variation in outcomes among extremely preterm infants is largely unexplained and may reflect differences in hospital practices regarding the initiation of active lifesaving treatment as compared with comfort care after birth. METHODS: We studied infants born between April 2006 and March 2011 at 24 hospitals included in the Eunice Kennedy Shriver National Institute of Child Health and Human Development Neonatal Research Network. Data were collected for 4987 infants born before 27 weeks of gestation without congenital anomalies. Active treatment was defined as any potentially lifesaving intervention administered after birth. Survival and neurodevelopmental impairment at 18 to 22 months of corrected age were assessed in 4704 children (94.3%). RESULTS: Overall rates of active treatment ranged from 22.1% (interquartile range [IQR], 7.7 to 100) among infants born at 22 weeks of gestation to 99.8% (IQR, 100 to 100) among those born at 26 weeks of gestation. Overall rates of survival and survival without severe impairment ranged from 5.1% (IQR, 0 to 10.6) and 3.4% (IQR, 0 to 6.9), respectively, among children born at 22 weeks of gestation to 81.4% (IQR, 78.2 to 84.0) and 75.6% (IQR, 69.5 to 80.0), respectively, among those born at 26 weeks of gestation. Hospital rates of active treatment accounted for 78% and 75% of the between-hospital variation in survival and survival without severe impairment, respectively, among children born at 22 or 23 weeks of gestation, and accounted for 22% and 16%, respectively, among those born at 24 weeks of gestation, but the rates did not account for any of the variation in outcomes among those born at 25 or 26 weeks of gestation. CONCLUSIONS: Differences in hospital practices regarding the initiation of active treatment in infants born at 22, 23, or 24 weeks of gestation explain some of the between-hospital variation in survival and survival without impairment among such patients. (Funded by the National Institutes of Health.).

Comments on "Intermediate and advanced topics in multilevel logistic regression analysis".

Multilevel random-effects models have become a popular method in the analysis of clustered data. Such analyses enable researchers to quantify within-cluster and between-cluster variations of an outcome and to separate individual-level and cluster-level effects of covariates by taking advantage of the hierarchical structure of clustered data. The tutorial article by Austin and Merlo1 was a timely effort intended to provide a comprehensive and up-to-date review of the tools and approaches. However, we feel that some important ideas and concepts described in this article need clarification.