Length of stay and readmission among late preterm infants: an instrumental variable approach

Hospital-Level NICU Capacity, Utilization, and 30-Day Outcomes in Texas

Importance

Risk-adjusted neonatal intensive care unit (NICU) utilization and outcomes vary markedly across regions and hospitals. The causes of this variation are poorly understood.

Objective

To assess the association of hospital-level NICU bed capacity with utilization and outcomes in newborn cohorts with differing levels of health risk.

Design, Setting, and Participants

This population-based retrospective cohort study included all Medicaid-insured live births in Texas from 2010 to 2014 using linked vital records and maternal and newborn claims data. Participants were Medicaid-insured singleton live births (LBs) with birth weights of at least 400 g and gestational ages between 22 and 44 weeks. Newborns were grouped into 3 cohorts: very low birth weight (VLBW; <1500 g), late preterm (LPT; 34-36 weeks' gestation), and nonpreterm newborns (NPT; ≥37 weeks' gestation). Data analysis was conducted from January 2022 to October 2023.

Exposure

Hospital NICU capacity measured as reported NICU beds/100 LBs, adjusted (ie, allocated) for transfers.

Main Outcomes and Measures

NICU admissions and special care days; inpatient mortality and 30-day postdischarge adverse events (ie, mortality, emergency department visit, admission, observation stay).

Results

The overall cohort of 874 280 single LBs included 9938 VLBW (5054 [50.9%] female; mean [SD] birth weight, 1028.9 [289.6] g; mean [SD] gestational age, 27.6 [2.6] wk), 63 160 LPT (33 684 [53.3%] female; mean [SD] birth weight, 2664.0 [409.4] g; mean [SD] gestational age, 35.4 [0.8] wk), and 801 182 NPT (407 977 [50.9%] female; mean [SD] birth weight, 3318.7 [383.4] g; mean [SD] gestational age, 38.9 [1.0] wk) LBs. Median (IQR) NICU capacity was 0.84 (0.57-1.30) allocated beds/100 LB/year. For VLBW newborns, NICU capacity was not associated with the risk of NICU admission or number of special care days. For LPT newborns, birth in hospitals with the highest compared with the lowest category of capacity was associated with a 17% higher risk of NICU admission (adjusted risk ratio [aRR], 1.17; 95% CI, 1.01-1.33). For NPT newborns, risk of NICU admission was 55% higher (aRR, 1.55; 95% CI, 1.22-1.97) in the highest- vs the lowest-capacity hospitals. The number of special care days for LPT and NPT newborns was 21% (aRR, 1.21; 95% CI,1.08-1.36) and 37% (aRR, 1.37; 95% CI, 1.08-1.74) higher in the highest vs lowest capacity hospitals, respectively. Among LPT and NPT newborns, NICU capacity was associated with higher inpatient mortality and 30-day postdischarge adverse events.

Conclusions and Relevance

In this cohort study of Medicaid-insured newborns in Texas, greater hospital NICU bed supply was associated with increased NICU utilization in newborns born LPT and NPT. Higher capacity was not associated with lower risk of adverse events. These findings raise important questions about how the NICU is used for newborns with lower risk.

Trends in morbidities of late preterm infants in the neonatal intensive care unit

OBJECTIVE

To characterize demographics and trends in length of stay (LOS), morbidities, and mortality in late preterm infants.

STUDY DESIGN

Cohort study of infants born between 34 0/7 and 36 6/7 weeks gestation between 1999 and 2018 without major congenital anomalies at Pediatrix Medical Group neonatal intensive care units (NICUs).

RESULTS

307,967 infants from 410 NICUs met inclusion criteria. The median (25th-75th percentile) LOS was 11 (8-16) days in the entire period. Postmenstrual age (PMA) at discharge increased during the cohort for all gestational ages (p < 0.001). There was a decrease in invasive ventilation, receipt of phototherapy, and reflux medications observed (p < 0.001).

CONCLUSION

In this large cohort, given 20 years of time for medical advancement, there was no significant improvement in the LOS of late preterm infants. All infants had an increased PMA at discharge, despite multiple practice changes that were observed.

Risk factors associated with 31-day unplanned hospital readmission in newborns: a systematic review

The purpose of this study is to synthesize evidence on risk factors associated with newborn 31-day unplanned hospital readmissions (UHRs). A systematic review was conducted searching CINAHL, EMBASE (Ovid), and MEDLINE from January 1st 2000 to 30th June 2021. Studies examining unplanned readmissions of newborns within 31 days of discharge following the initial hospitalization at the time of their birth were included. Characteristics of the included studies examined variables and statistically significant risk factors were extracted from the inclusion studies. Extracted risk factors could not be pooled statistically due to the heterogeneity of the included studies. Data were synthesized using content analysis and presented in narrative and tabular form. Twenty-eight studies met the eligibility criteria, and 17 significant risk factors were extracted from the included studies. The most frequently cited risk factors associated with newborn readmissions were gestational age, postnatal length of stay, neonatal comorbidity, and feeding methods. The most frequently cited maternal-related risk factors which contributed to newborn readmissions were parity, race/ethnicity, and complications in pregnancy and/or perinatal period.

CONCLUSION

This systematic review identified a complex and diverse range of risk factors associated with 31-day UHR in newborn. Six of the 17 extracted risk factors were consistently cited by studies. Four factors were maternal (primiparous, mother being Asian, vaginal delivery, maternal complications), and two factors were neonatal (male infant and neonatal comorbidities). Implementation of evidence-based clinical practice guidelines for inpatient care and individualized hospital-to-home transition plans, including transition checklists and discharge readiness assessments, are recommended to reduce newborn UHRs.

WHAT IS KNOWN

• Attempts have been made to identify risk factors associated with newborn UHRs; however, the results are inconsistent.

WHAT IS NEW

• Six consistently cited risk factors related to newborn 31-day UHRs. Four maternal factors (primiparous, mother being Asian, vaginal delivery, maternal complications) and 2 neonatal factors (male infant and neonatal comorbidities). • The importance of discharge readiness assessment, including newborn clinical fitness for discharge and parental readiness for discharge. Future research is warranted to establish standardised maternal and newborn-related variables which healthcare providers can utilize to identify newborns at greater risk of UHRs and enable comparison of research findings.

Incidence, Risk Factors, and Reasons for 30-Day Hospital Readmission Among Healthy Late Preterm Infants

OBJECTIVE

Late preterm infants have an increased risk of morbidity relative to term infants. We sought to determine the rate, temporal trend, risk factors, and reasons for 30-day readmission.

METHODS

This is a retrospective cohort study of infants born at 34 to 42 weeks' gestation in California between January 1, 2011, and December 31, 2017. Birth certificates maintained by California Vital Statistics were linked to discharge records maintained by the California Office of Statewide Health Planning and Development. Multivariable logistic regression was used to identify risk factors and derive a predictive model.

RESULTS

Late preterm infants represented 4.3% (n = 122 014) of the study cohort (n = 2 824 963), of which 5.9% (n = 7243) were readmitted within 30 days. Compared to term infants, late preterm infants had greater odds of readmission (odds ratio [OR]: 2.34 [95% confidence interval (CI): 2.28-2.40]). The temporal trend indicated increases in all-cause and jaundice-specific readmission infants (P < .001). The common diagnoses at readmission were jaundice (58.9%), infections (10.8%), and respiratory complications (3.5%). In the adjusted model, factors that were associated with greater odds of readmission included assisted vaginal birth, maternal age ≥34 years, diabetes, chorioamnionitis, and primiparity. The model had predictive ability of 60% (c-statistic 0.603 [95% CI: 0.596-0.610]) in late preterm infants who had <5 days length of stay at birth.

CONCLUSION

The findings contribute important information on what factors increase or decrease the risk of readmission. Longitudinal studies are needed to examine promising hospital predischarge and follow-up care practices.

Neonatal Intensive Care Utilization and Postdischarge Newborn Outcomes: A Population-based Study of Texas Medicaid Insured Infants

OBJECTIVE

To test the hypothesis that newborn infants cared for in hospitals with greater utilization of neonatal intensive care experienced fewer postdischarge adverse events.

STUDY DESIGN

We developed 3 retrospective population-based cohorts of Texas Medicaid insured singletons born in 2010-2014 (very low birth weight [VLBW n = 11 139], late preterm [n = 57 509], and non-preterm [n = 664 447]) who received care in higher volume hospitals with level III/IV neonatal intensive care units (NICUs). Measures of NICU care were hospital-level risk adjusted NICU admission rates, special care days (days of nonroutine care) per infant, and the percent of intensive (highest billable care code) special care days. The units of analysis were hospitals (n = 80) and the primary outcome was an adverse event, (defined as admission, emergency department visit, or death) within 30 days postdischarge.

RESULTS

Higher use of NICU care at a hospital level was not associated with lower postdischarge 30-day adverse event. Infants cared for in hospitals with above vs below median special care day rates experienced slightly higher postdischarge adverse event per 100 infants (VLBW: 14.01 [95% CI 12.74-15.27] vs 11.84 [10.52-13.16], P < .05; late preterm: 7.33 [6.68-7.97] vs 6.28 [5.87-6.69], P < .01; non-preterm: 4.47 [4.17-4.76] vs 3.97 [3.75-4.18], P < .01). Weak positive associations (Pearson correlations of 0.31-0.37, P < .01) were observed for adverse event with special care days; in no instance was a negative association observed between NICU utilization and adverse event.

CONCLUSION

Higher utilization of NICU care was not associated with lower rates of short-term events suggesting that there may be opportunities to safely decrease admission rates and length of NICU stays.

Maternal and Perinatal Determinants of Late Hospital Discharge Among Late Preterm Infants; A 5-Year Cross-Sectional Analysis

Background: Although late preterm infants (LPIs) account for the majority of preterm births, they are mistakenly labelled and treated as "near term." Whether longer initial hospital stay improves their outcomes and lowers readmission is controversial. The aim of this study is to identify maternal and perinatal factors associated with longer hospital stay and to assess the rate of readmission. Methods: The medical records of LPIs delivered at an academic center in Jordan over a 5-year period were reviewed. They were divided according to their initial hospital stay into: Early discharge group (ED, ≤ 3 days) and late discharge group (LD, > 3 days). Maternal and perinatal factors associated with > 3-day hospital stay were reported. The rate of readmission was compared between both groups. Results: 2236 LPIs were included in the analysis representing 13% of total births and 81% of premature births. LD group constituted 54%. A thousand two hundred forty three (56%) required admission to NICU. Factors associated with longer hospital stay included maternal prolonged rupture of membranes (AOR 1.9, 95% C.I 1.5, 2.4, p 0.000), C-section delivery (AOR 2.4, 95% C.I 1.9, 3, p 0.001), <35-week gestation (AOR 3.8, 95% C.I 2.6, 5, p 0.000), small-for-gestational age (AOR 1.9, 95% C.I 1.1, 3.8, p 0.03), birthweight <2,500 g (AOR 1.3, 95% C.I 1.1, 1.6, p 0.02), NICU admission (AOR 6.3, 95% C.I 3.4, 11.5, p 0.000), RDS (AOR 2.3, 95% C.I 1.5, 3.6, p 0.005), surfactant therapy (AOR 5, 95% C.I 1.9, 13.5, p 0.001), use of CPAP (AOR 1.7, 95% C.I 1.2, 2.2, p 0.001), jaundice (AOR 11.2, 95% C.I 7.7, 16.2, p 0.000), and sepsis (AOR 10.3, 95% C.I 4.8, 22, p 0.000). Readmission rate was 19% among the LD group and 13% among the ED group. Conclusion: LPIs are at high risk for developing prematurity-related morbidities and the duration of their initial hospital stay can be anticipated based on certain predisposing maternal and perinatal factors. Late discharge of LPIs does not lower the rate of readmission.

Hospital Care Cost and Resource Use of Early Discharge of Healthy Late Preterm and Term Singletons: A Population-based Cohort Study and Cost Analysis

OBJECTIVE

To assess the hospital care cost and resource use associated with discharge timings after late preterm and term births.

STUDY DESIGN

This population-based cohort study and cost analysis included all healthy singleton late preterm (35-36 weeks gestational age) and term infants (37-41 weeks gestational age) born vaginally in hospitals in Ontario, Canada, from 2003 to 2012. Early, late, and very late discharge (<48, 48-71, and 72-95 hours after birth, respectively) were compared using generalized linear models. The primary outcome was the total hospital care cost (hospitalizations and emergency department visits) per infant within 28 days of birth.

RESULTS

Among 860 693 singletons (3.7% late preterm), early discharge increased significantly over 10 years for term infants (from 69% to 82%; P < .001), but not late preterm infants (from 32% to 35%; P = .75). The mean total cost within 28 days after birth was not significantly different for late preterm infants between early discharge and late discharge after adjustment. However, for term infants, the adjusted cost was higher with early discharge than late discharge (aMCD $311 [95% CI, $211-$412] per infant; $366 [95% CI, $355-$377] per mother-infant dyad). The neonatal readmission rates were higher after early than late discharge for late preterm and term infants.

CONCLUSIONS

Early discharge was not associated with cost savings for vaginally born healthy singleton late preterm infants, and instead was associated with a cost increase for term infants. Early discharge was associated with higher neonatal readmission rates. Individualized approach balancing the risk and benefit is appropriate to determine the discharge timings.

Neonatal Intensive Care Variation in Medicaid-Insured Newborns: A Population-Based Study

OBJECTIVE

To assess the contribution of maternal and newborn characteristics to variation in neonatal intensive care use across regions and hospitals.

STUDY DESIGN

This was a retrospective population-based live birth cohort of newborn infants insured by Texas Medicaid in 2010-2014 with 2 subcohorts: very low birth weight (VLBW) singletons and late preterm singletons. Crude and risk-adjusted neonatal intensive care unit (NICU) admission rates, intensive and intermediate special care days, and imaging procedures were calculated across Neonatal Intensive Care Regions (n = 21) and hospitals (n = 100). Total Medicaid payments were calculated.

RESULTS

Overall, 11.5% of live born, 91.7% of VLBW, and 37.6% of infants born late preterm were admitted to a NICU, receiving an average of 2 days, 58 days, and 5 days of special care with payments per newborn inpatient episode of $5231, $128 075, and $10 837, respectively. There was little variation across regions and hospitals in VLBW NICU admissions but marked variation for NICU admissions in late preterm newborn infants and for special care days and imaging rates in all cohorts. The variation decreased slightly after health risk adjustment. There was moderate substitution of intermediate for intensive care days across hospitals (Pearson r VLBW -0.63 P < .001; late preterm newborn -0.53 P < .001).

CONCLUSIONS

Across all risk groups, the variation in NICU use was poorly explained by differences in newborn illness levels and is likely to indicate varying practice styles. Although the "right" rates are uncertain, it is unlikely that all of these use patterns represent effective and efficient care.

Risk factors associated with paediatric unplanned hospital readmissions: a systematic review

OBJECTIVE

To synthesise evidence on risk factors associated with paediatric unplanned hospital readmissions (UHRs).

DESIGN

Systematic review.

DATA SOURCE

CINAHL, EMBASE (Ovid) and MEDLINE from 2000 to 2017.

ELIGIBILITY CRITERIA

Studies published in English with full-text access and focused on paediatric All-cause, Surgical procedure and General medical condition related UHRs were included.

DATA EXTRACTION AND SYNTHESIS

Characteristics of the included studies, examined variables and the statistically significant risk factors were extracted. Two reviewers independently assessed study quality based on six domains of potential bias. Pooling of extracted risk factors was not permitted due to heterogeneity of the included studies. Data were synthesised using content analysis and presented in narrative form.

RESULTS

Thirty-six significant risk factors were extracted from the 44 included studies and presented under three health condition groupings. For All-cause UHRs, ethnicity, comorbidity and type of health insurance were the most frequently cited factors. For Surgical procedure related UHRs, specific surgical procedures, comorbidity, length of stay (LOS), age, the American Society of Anaesthesiologists class, postoperative complications, duration of procedure, type of health insurance and illness severity were cited more frequently. The four most cited risk factors associated with General medical condition related UHRs were comorbidity, age, health service usage prior to the index admission and LOS.

CONCLUSIONS

This systematic review acknowledges the complexity of readmission risk prediction in paediatric populations. This review identified four risk factors across all three health condition groupings, namely comorbidity; public health insurance; longer LOS and patients<12 months or between 13-18 years. The identification of risk factors, however, depended on the variables examined by each of the included studies. Consideration should be taken into account when generalising reported risk factors to other institutions. This review highlights the need to develop a standardised set of measures to capture key hospital discharge variables that predict unplanned readmission among paediatric patients.

Newborn Length of Stay and Risk of Readmission

BACKGROUND

Evidence on the association between newborn length of hospital stay (LOS) and risk of readmission is conflicting. We compared methods for modelling this relationship, by gestational age, using population-level hospital data on births in England between 2005-14.

METHODS

The association between LOS and unplanned readmission within 30 days of postnatal discharge was explored using four approaches: (i) modelling hospital-level LOS and readmission rates; (ii) comparing trends over time in LOS and readmission; (iii) modelling individual LOS and adjusted risk of readmission; and (iv) instrumental variable analyses (hospital-level mean LOS and number of births on the same day).

RESULTS

Of 4 667 827 babies, 5.2% were readmitted within 30 days. Aggregated data showed hospitals with longer mean LOS were not associated with lower readmission rates for vaginal (adjusted risk ratio (aRR) 0.87, 95% confidence interval (CI) 0.66, 1.13), or caesarean (aRR 0.89, 95% CI 0.72, 1.12) births. LOS fell by an average 2.0% per year for vaginal births and 3.4% for caesarean births, while readmission rates increased by 4.4 and 5.1% per year respectively. Approaches (iii) and (iv) indicated that longer LOS was associated with a reduced risk of readmission, but only for late preterm, vaginal births (34-36 completed weeks' gestation).

CONCLUSIONS

Longer newborn LOS may benefit late preterm babies, possibly due to increased medical or psychosocial support for those at greater risk of potentially preventable readmissions after birth. Research based on observational data to evaluate relationships between LOS and readmission should use methods to reduce the impact of unmeasured confounding.

Effect of prophylactic CPAP in very low birth weight infants in South America

OBJECTIVE

The objective of this study was to examine the effect of prophylactic continuous positive airway pressure (CPAP) on infants born in 25 South American neonatal intensive care units affiliated with the Neocosur Neonatal Network using novel multivariate matching methods.

STUDY DESIGN

A prospective cohort was constructed of infants with a birth weight 500 to 1500 g born between 2005 and 2011 who clinically were eligible for prophylactic CPAP. Patients who received prophylactic CPAP were matched to those who did not on 23 clinical and sociodemographic variables (N=1268). Outcomes were analyzed using the McNemar's test.

RESULTS

Infants not receiving prophylactic CPAP had higher mortality rates (odds ratio (OR)=1.69, 95% confidence interval (CI) 1.17, 2.46), need for any mechanical ventilation (OR=1.68, 95% CI 1.33, 2.14) and death or bronchopulmonary dysplasia (BPD) (OR=1.47, 95% CI 1.09, 1.98). The benefit of prophylactic CPAP varied by birth weight and gender.

CONCLUSIONS

The implementation of this process was associated with a significant improvement in survival and survival free of BPD.

Breastfeeding Continuation Among Late Preterm Infants: Barriers, Facilitators, and Any Association With NICU Admission?

BACKGROUND AND OBJECTIVES

Late preterm birth (at 34-36 6/7 weeks' gestation) is a risk factor for early breastfeeding cessation. The objective of this study was to determine barriers to and facilitators of breastfeeding continuation among late preterm infants (LPI) and to compare the barriers faced by LPI admitted to the well nursery versus the NICU.

METHODS

The SAS Complex Survey was used to perform multivariable logistic regression analysis by using data from the Centers for Disease Control and Prevention's Pregnancy Risk Assessment Monitoring System. Data from 3 states (Illinois, Maine, and Vermont) for the years 2004 to 2008 were used.

RESULTS

A total of 2530 mothers of LPI were surveyed. Odds of breastfeeding initiation were similar among LPI admitted to the NICU versus the well nursery (adjusted odds ratio, 1.24 [95% confidence interval, 0.88-1.73]; P = .209). Odds of breastfeeding for ≥ 10 weeks were no different between LPI admitted to the NICU versus those admitted to the well-nursery (adjusted odds ratio, 1.02 [95% confidence interval, 0.73-1.43]; P = .904). Factors associated with increased odds of breastfeeding for ≥ 10 weeks among LPI were higher maternal education, mother being married, and normal maternal BMI. Regardless of NICU admission, the top reasons cited by mothers of LPI for early breastfeeding discontinuation were perceived inadequate milk supply and nursing difficulties.

CONCLUSIONS

Among LPIs, NICU admission was not associated with early breastfeeding cessation. Mothers of LPIs with lower odds of sustaining breastfeeding for at least 10 weeks were single mothers, those with a high school education only, and those who were obese. Breastfeeding support should be enhanced for LPIs and should address perceived maternal milk supply concerns and nursing difficulties.

Risk of Hospital Readmission Among Infants With Neonatal Abstinence Syndrome

OBJECTIVE

Neonatal abstinence syndrome (NAS) is a postnatal drug withdrawal syndrome that may last for months. Our objective was to determine if infants with NAS are at increased risk for hospital readmission compared with uncomplicated term and late preterm newborns.

METHODS

In this longitudinal retrospective cohort study, administrative data were used for all births from 2006 to 2009 in the New York State Inpatient Database. We identified infants with NAS, born late preterm or uncomplicated term, as independent groups using diagnostic codes and determined readmission rates. We fit a multivariable logistic regression model with 30-day readmission after discharge as the outcome and infant characteristics, clinical morbidities, insurance type, and length of birth hospitalization as predictors.

RESULTS

From 2006 to 2009 in New York State, 700 613 infants were classified as uncomplicated term, 51 748 were born late preterm, and 1643 infants were diagnosed with NAS. After adjusting for confounders, infants with NAS (odds ratio [OR] 2.49, 95% confidence interval [CI] 1.75-3.55) were more likely than uncomplicated term infants to be readmitted within 30 days of birth hospitalizations. The risk of readmission was similar to late preterm infants (OR 2.26, 95% CI 2.09-2.45). Length of birth hospitalization in days was inversely related to odds of being readmitted within 30 days of birth hospitalization (OR 0.94 95% CI 0.92-0.96).

CONCLUSIONS

When compared with uncomplicated term infants, infants diagnosed with NAS were more than twice as likely to be readmitted to the hospital. Future research and state-level policies should investigate means to mitigate risk of hospital readmission for infants with NAS.

Challenges to measuring variation in readmission rates of neonatal intensive care patients

OBJECTIVE

To examine the viability of a hospital readmission quality metric for infants requiring neonatal intensive care.

METHODS

Two cohorts were constructed. First, a cohort was constructed from infants born in California from 1995 to 2009 at 23 to 34 weeks' gestation, using birth certificates linked to maternal and infant inpatient records (N = 343,625). Second, the Medicaid Analytic eXtract (MAX) identified Medicaid-enrolled infants admitted to the neonatal intensive care unit (NICU) during their birth hospitalization in 18 states during 2006 to 2008 (N = 254,722). Hospital and state-level unadjusted readmission rates and rates adjusted for gestational age, birth weight, insurance status, gender, and common complications of preterm birth were calculated.

RESULTS

Within California, there were wide variations in hospital-level readmission rates that were not completely explained through risk adjustment. Similar unadjusted variation was seen between states using MAX data, but risk adjustment and calculation of hospital-level rates were not possible because of missing gestational age, birth weight, and birth hospital data.

CONCLUSIONS

The California cohort shows significant variation in hospital-level readmission rates after risk adjustment, supporting the premise that readmission rates of prematurely born infants may reflect care quality. However, state data do not include term and early term infants requiring neonatal intensive care. MAX allows for multistate comparisons of all infants requiring NICU care. However, there were extensive missing data in the few states with sufficient information on managed care patients to calculate state-level measures. Constructing a valid readmission measure for NICU care across diverse states and regions requires improved data collection, including potential linkage between MAX data and vital statistics records.

Factors associated with readmission in late-preterm infants: a matched case-control study

OBJECTIVE

The goal of this study was to evaluate risk factors for readmission among late-preterm (34-36 weeks' gestation) infants in clinical practice.

METHODS

This was a retrospective, matched case-control study of late-preterm infants receiving care across 8 regional hospitals in 2009 in the United States. Those readmitted within 28 days of birth were matched to non-readmitted infants at a ratio of 1:3 according to birth hospital, birth month, and gestational age. Step-wise modeling with likelihood ratio tests were used to develop a multivariable logistic regression model. A subgroup analysis of hyperbilirubinemia readmissions was also performed.

RESULTS

Of 1861 late-preterm infants delivered during the study period, 67 (3.6%) were readmitted within 28 days of birth. These were matched to 201 control infants, for a final sample of 268 infants. In multivariable regression, each additional day in length of stay was associated with a significantly reduced odds ratio (OR) for readmission (0.57, P = .004); however, for those infants delivered vaginally, there was no significant association between length of stay and readmission (adjusted OR: 1.08, P = .16). A stronger inverse relationship was observed in subgroup analysis for hyperbilirubinemia readmissions, with the adjusted OR associated with increased length of stay 0.40 (P = .002) for infants born by cesarean delivery but 1.14 (P = .27) for those delivered vaginally.

CONCLUSIONS

Infants born via cesarean delivery with longer length of hospital stay have a decreased risk for readmission. As hospitals implement protocols to standardize length of stay, mode of delivery may be a useful factor to identify late-preterm infants at higher risk for readmission.

Instrumental variable methods for causal inference

A goal of many health studies is to determine the causal effect of a treatment or intervention on health outcomes. Often, it is not ethically or practically possible to conduct a perfectly randomized experiment, and instead, an observational study must be used. A major challenge to the validity of observational studies is the possibility of unmeasured confounding (i.e., unmeasured ways in which the treatment and control groups differ before treatment administration, which also affect the outcome). Instrumental variables analysis is a method for controlling for unmeasured confounding. This type of analysis requires the measurement of a valid instrumental variable, which is a variable that (i) is independent of the unmeasured confounding; (ii) affects the treatment; and (iii) affects the outcome only indirectly through its effect on the treatment. This tutorial discusses the types of causal effects that can be estimated by instrumental variables analysis; the assumptions needed for instrumental variables analysis to provide valid estimates of causal effects and sensitivity analysis for those assumptions; methods of estimation of causal effects using instrumental variables; and sources of instrumental variables in health studies.