Does Timing Matter? A National Perspective on the Risk of Incarceration inPremature Neonates with Inguinal Hernia

Timothy B. Lautz, MD, Mehul V. Raval, MD, MS, and Marleta Reynolds, MD

Objectives To determine the incidence of inguinal hernia in premature neonates and identify risk factors for incar-ceration.Study design The 2003 and 2006 Kids’ Inpatient Databases were queried for diagnoses indicative of prematurebirth and inguinal hernia.Results Inguinal hernia was diagnosed during the birth hospitalization in 1463 � 87 of 49 273 � 1561 prematureneonates (3%). Male sex, gestational age, birth weight, and prolonged mechanical ventilation were associated withinguinal hernia (all P < .01). Incarceration occurred in 176 of 1123 premature neonates (16%) who underwent herniarepair during the birth hospitalization. Delaying repair beyond 40 weeks post-conceptual age doubled the risk ofincarceration (21%), as compared with 36 to 39 weeks (9%) or <36 weeks (11%, P = .002). Sex, race, and insurancewere not associated with incarceration.Conclusion The risk of incarceration is doubled in premature neonates with inguinal hernia when repair is delayedbeyond 40 weeks post-conceptual age. This increased incarceration risk should be one of the factors consideredwhen deciding on the optimal timing of inguinal hernia repair. (J Pediatr 2011;158:573-7).

Prematurity is associated with an increased risk of inguinal hernia because of a persistent processes vaginalis that typicallycloses during the last weeks of gestation.1 Management of premature neonates with inguinal hernia presents a dilemma.Technical challenges, co-morbid conditions, and potential anesthetic and surgical complications in these extremely

small neonates motivate delaying of the operation.2,3 However, longer delays may increase the risk of incarceration, with po-tential for bowel strangulation or testicular atrophy.2,4,5 Repeated herniation and reduction may also increase scarring, makingthe operation more difficult and the risk of complications greater.6 In balancing these dueling considerations, surgery is oftenperformed just before expected discharge from the neonatal intensive care unit (NICU).1,4,7,8 Most pediatric surgeons favoringuinal hernia repair before discharge, even in neonates born before 30 weeks, because of the high risk of incarceration inthe first year of life.9 However, it has been suggested that even waiting until hospital discharge may unnecessarily increasethe risk of incarceration, and earlier repair may be warranted.10

We sought to investigate the occurrence of inguinal hernia in premature neonates during their initial birth hospitalization byusing a weighted national data set. The aim of the study was two-fold: (1) to delineate the scope of this problem as it relates tosex, race, gestational age, and birth weight; and (2) to determine whether the timing of operative repair is associated with anincreased risk of incarceration.

AHRQ Agency for Healthcare Re

GA Gestational age

HCUP Healthcare Cost and Utili

ICD-9-CM International Classification

KID Kids’ Inpatient Database

NICU Neonatal intensive care u

Methods

Data on US children with diagnoses of prematurity and inguinal hernia in the years 2003 and 2006 were obtained from theAgency for Healthcare Research and Quality (AHRQ)-sponsored Healthcare Cost and Utilization Project (HCUP) Kids’ Inpa-tient Database (KID). The KID is an administrative data set of patients, age #20 years, and currently contains data on >10million hospitalizations from 38 states. Versions of the KID are released in 3-year cycles, and the two most recent release dateswere used in this study. The KID uses a sampling of pediatric discharges, and data are subsequently weighted to produce na-tional estimates on outcomes of interest. The KID samples 10% of routine births and 80% of pediatric cases from each framehospital. The KID is estimated to capture 87% of the US pediatric population.

Neonates with a diagnosis of prematurity were identified in the KID by the International Classification of Disease, Ninth Re-vision, Clinical Modification (ICD-9-CM) diagnosis codes 765.00 to 765.28. Patients with a diagnosis of prematurity were fur-

From the Department of Surgery, Children’s MemorialHospital, Northwestern University, Chicago, IL

The authors declare no conflicts of interest.

0022-3476/$ - see front matter. Copyright ª 2011 Mosby Inc.

All rights reserved. 10.1016/j.jpeds.2010.09.047

search and Quality

zation Project

of Disease, Ninth Revision, Clinical Modification

nit

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Table I. Estimated incidence of inguinal hernia inpremature neonates hospitalized >28 days in the year2006

Herniadiagnosis Incidence

Pvalue

All premature infants (n = 49 273 � 1561) 1463 � 87 2.97%Sex <.001

Male (n = 25 607 � 807) 1157 � 68 4.52%Female (n = 23 666 � 779) 306 � 32 1.29%

Race .041Caucasian (n = 17 434 � 888) 587 � 46 3.37%African-American (n = 8084 � 484) 274 � 23 3.39%Hispanic (n = 7539 � 495) 200 � 23 2.65%Other (n = 3639 � 188) 125 � 14 3.44%

Prolonged mechanical ventilation(>96 hours)

<.001

Yes (n = 15 521 � 631) 681 � 50 4.39%No (n = 33 766 � 1079) 782 � 52 2.32%

Gestational age <.001<24 weeks (n = 563 � 39) 30 � 7 5.32%24 weeks (n = 1430 � 81) 95 � 14 6.64%25-26 weeks (n =5229 � 243) 310 � 29 5.93%27-28 weeks (n = 8420 � 320) 314 � 27 3.73%29-30 weeks (n = 12453 � 428) 316 � 26 2.54%31-32 weeks (n = 10691 � 353) 180 � 19 1.68%33-34 weeks (n = 3716 � 152) 66 � 11 1.78%35-36 weeks (n = 1561 � 77) 20 � 6 1.28%

Birth weight <.001<1000 g (n = 13 755 � 556) 774 � 56 5.63%>1000 g (n = 34 105 � 1054) 636 � 45 1.86%

THE JOURNAL OF PEDIATRICS � www.jpeds.com Vol. 158, No. 4

ther stratified according to demographic and clinical fea-tures, including sex, race, and primary payer. Gestationalage was determined from the fifth digit of the ICD-9-CM765.2 diagnosis code. The KID has a unique field for birthweight. In cases in which this field was not populated,birth-weight was estimated from the fifth digits of the ICD-9-CM 765.0 and 765.1 diagnosis codes. ICD-9-CM codes765.00 to 765.03 and 765.10 to 765.13 were indicative of pre-maturity with weight <1000 g, and codes 765.04 to 765.09and 765.14 to 765.19 indicated weight >1000 g. Prolongedmechanical ventilation (>96 hours), a potential risk factorfor hernia, was identified with ICD-9-CM procedure code96.72.

The diagnosis of inguinal hernia was established by ICD-9-CM diagnosis codes and stratified into incarcerated (550.0and 550.1) versus non-incarcerated (550.9) hernias. Patientswho underwent an operation for inguinal hernia were iden-tified with ICD-9-CM procedure codes and classified by ex-tent of disease in unilateral (53.0) versus bilateral (53.1)repair. For each procedure code in the KID, there is a field in-dicating the number of days from admission until that pro-cedure. This field was used to determine the time frombirth (admission) until hernia repair.

In children with a diagnosis of prematurity, the occurrenceof inguinal hernia diagnosis, repair, or both was consideredto have occurred during the initial birth hospitalizationwhen it occurred during the in-hospital birth encounter orwhen the patient was admitted as a transfer from another in-stitution (admission source from another hospital) beforethe fifth day of life.

We next analyzed predictors of incarceration. Whereas theaforementioned national estimates used weighted valuesfrom the 2006 KID, these comparisons used discreet casesfrom the 2003 and 2006 data sets. Clinical factors predictiveof increased incarceration risk, including sex, race, primaryinsurance provider, gestational age, and birth weight, wereanalyzed during the initial birth hospitalization. Absolutetime from birth until hernia repair and the post-conceptualage at surgery were investigated for association with an in-creased incarceration risk. The mean post-conceptual age atthe time of surgery was estimated by adding the gestationalage at birth to the time from birth until surgery. The gesta-tional age at birth is coded in 2-week intervals (eg, ICD-9-CM code 765.23 = 25-27 weeks gestation). For the purposesof this calculation, the earliest possible gestational age wasused. Incarceration was determined with a diagnosis codefor incarcerated hernia during the hospital admission.Finally, the rate of incarceration was compared between pre-mature neonates undergoing hernia repair during the initialbirth hospitalization and all other children undergoing ingui-nal hernia repair in the first year of life.

Statistical AnalysisWeighted national estimates accounting for hospital strata,clustering, and discharge weight were calculated with thecomplex samples module of SPSS software version 18(SPSS Corporation, Chicago, Illinois). Results were

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expressed as a mean and standard error. Patient- andhospital-specific factors predictive of incarceration were an-alyzed with c

2 analysis for categorical data and an indepen-dent samples t test for continuous variables. All analyseswere two-tailed, and statistical significance was set at P <.05. The study protocol was approved by the NorthwesternUniversity Institutional Review Board.

Results

Inguinal hernia was diagnosed in 1463� 87 of 49 273� 1561premature neonates (2.97%), with a 3.5-fold male prepon-derance (Table I). The incidence was highest for neonatesborn at 24 to 26 weeks gestation (5.9%-6.6%), which wasabout 4-fold higher than for neonates born at 33 to 36weeks (1.3%-1.8%). Likewise, the rate in extremely lowbirth weight (<1000 g) infants was 5.6%, compared with1.9% in infants with birth weight >1000 g. Prolongedmechanical ventilation doubled the risk of inguinal herniafrom 2.3% to 4.9%.

Incarceration Risk During the Hospitalization ofBirthDuring the 2 years studied, there were 2009 unweighted casesof inguinal hernia diagnosed in premature neonates duringtheir initial hospitalization. Repair was performed in 1123(55.9%) of these neonates, 884 (78.7%) of whom weremale, 888 (79.1%) who underwent bilateral repair, and 176(15.7%) in whom incarceration was diagnosed. The meanoverall length of hospital stay was 82.7 � 38.4 days, and

Lautz, Raval, and Reynolds

Table III. Relationship between timing of hernia repairand rate of incarceration

Incarcerated Non-incarcerated P value

Days from birth to repair,mean � SEM

76.7 � 44.5 67.8 � 33.0 .046

Interval .285#1 month 13 (10.2%) 76 (10.5%)1-2 months 32 (25.2%) 238 (32.9%)2-3 months 46 (36.2%) 248 (34.3%)>3 months 36 (28.3%) 162 (22.4%)

Post-conceptual age at repair .002<36 weeks 28 (31.8%) 220 (33.4%)36-39 weeks 33 (37.5%) 335 (50.8%)40+ weeks 27 (30.7%) 104 (15.8%)

Hospitalization at repair <.001Initial (birth) hospitalization 176 (15.4%) 947 (27.6%)Subsequent hospitalization* 968 (84.6%) 2487 (72.4%)

*In all children within the first year of life.

April 2011 ORIGINAL ARTICLES

hernia repair was performed after an average of 69.6 � 34.0days. The mean post-conceptual age at the time of surgerywas 37.4 � 3.4 weeks, and 131 of 747 subjects (17.5%)were at least 40 weeks post-conception at the time of surgery.

The demographics and clinical features of neonates oper-ated on for incarcerated and non-incarcerated hernias arecompared in Table II. Sex, race, insurance coverage,prolonged mechanical ventilation, gestational age, andbirth weight had no statistically significant effect on therisk of incarceration.

The relationship between operative timing and rate of in-carceration was analyzed. In children who underwent herniarepair during the initial hospitalization, the mean time frombirth to operation was higher (75.9 � 39.9 days) in childrenwith incarceration, as compared to children with non-incarcerated hernia (68.5 � 32.8 days, P = .05; Table III).Stratifying newborns in clinically relevant time intervalsfrom birth to repair, the rate of incarceration was 14.6%before 1 month, 11.9% at 1 to 2 months, 15.6% at 2 to 3months, and 18.2% for repair after 3months of life (P= .285).

We likewise analyzed the relationship between estimatedpost-conceptual age at the time of surgery and the risk of in-carceration. Themean post-conceptual age at the time of sur-gery was similar in patients with incarcerated (37.7 weeks �4.2 days) and non-incarcerated (37.3 weeks � 3.3 days)hernia (P = .382). However, repair after 40 weeks post-conception was associated with a 2-fold risk of incarceration(27/131, 20.6%) compared with repair between 36 and 40

Table II. Demographics and clinical features ofpremature infants undergoing surgery for incarceratedand non-incarcerated inguinal hernias during initialhospitalization

Incarcerated(n = 176)

Non-incarcerated(n = 947)

Pvalue

Sex .770Male 140 (79.5%) 744 (78.6%)Female 36 (20.5%) 203 (21.4%)

Race .952Caucasian 70 (51.1%) 393 (51.8%)African-American 36 (26.3%) 178 (23.5%)Hispanic 20 (14.6%) 109 (14.4%)Other 11 (8.0%) 79 (10.4%)

Insurance .637Medicaid 74 (43.8%) 374 (41.8%)Private 95 (56.2%) 520 (58.2%)

Prolonged mechanicalventilation (>96 hours)

.173

Yes 97 (55.1%) 469 (49.5%)No 79 (44.9%) 478 (50.5%)

Gestational age .496<24 weeks 3 (2.4%) 16 (1.9%)24 weeks 8 (6.4%) 66 (7.9%)25-26 weeks 38 (30.4%) 206 (24.7%)27-28 weeks 27 (21.6%) 203 (24.4%)29-30 weeks 21 (16.8%) 160 (19.2%)31-32 weeks 18 (14.4%) 100 (12.0%)33-34 weeks 9 (7.2%) 49 (5.9%)35-36 weeks 1 (0.8%) 33 (4.0%)

Birth weight .631<1000 g 66 (38.6%) 341 (36.7%)>1000 g 105 (61.4%) 589 (63.3%)

Does Timing Matter? A National Perspective on the Risk of Incar

weeks (33/368, 9.0%; P < .001) or before 36 weeks (28/248,11.3%; P = .014).

Incarceration Risk After the Initial Hospitalization inthe First Year of LifeAs described above, 886 (44.1%) premature neonates witha diagnosis of inguinal hernia did not undergo repair duringthe initial hospitalization. Because longitudinal data is notavailable in the KID, the 15.7% rate of incarceration in neo-nates who underwent an operation during the initial hospi-talization was compared with the rate of incarceration in allchildren undergoing hernia repair during a subsequent(non-birth) hospitalization within the first year of life. Of3455 premature and term infants who underwent inguinalhernia repair during a subsequent admission in the firstyear of life, 968 (28.0%) had a diagnosis of incarceration.This figure includes both premature and term infants, but of-fers insight in the potential increased incarceration risk whenrepair is delayed after the initial hospitalization.

Discussion

On the basis of estimates from a large administrative data set,3% of all premature infants hospitalized after 28 days of lifewill have a clinically evident inguinal hernia. Male sex, pro-longed mechanical ventilation, lower gestational age, and ex-tremely low birth weight are associated with an increased riskof inguinal hernia (all P < .01). The rate of incarceration islower in premature infants who undergo operative repairduring their initial hospitalization (15.7%) compared withall infants who otherwise undergo inguinal hernia repairwithin the first year of life (28.0%). Within the initial hospi-talization, the interval from birth to repair has no significantbearing on the risk of incarceration. However, delaying repairafter 40 weeks post-conceptual age increases the risk of incar-ceration 2-fold (P < .001).The incidence of inguinal hernia reported only reflects oc-

currences during the initial hospitalization of birth or in-stances in which the newborn was transferred within the

ceration in Premature Neonates with Inguinal Hernia 575

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first 5 days of life. It is also limited to patients hospitalized>28 days to avoid biasing the data with extremely low gesta-tional age infants who die before consideration of hernia re-pair or near-term infants who are discharged beforemanifesting a hernia. Although our analysis does not distin-guish the location of these neonates within the hospital, it isexpected to closely mirror studies addressing the incidence ofinguinal hernia and risk of incarceration within the NICU.The in-hospital incidence of 3% reported is lower thanwhat has been reported from single institutions.11,12 Thisstudy may be more indicative of the true national rate thansingle institution series that may care for a disproportionatenumber of surgical referrals. This study also better delineatesthe well-accepted inverse correlation between gestational age(or birth weight) and hernia risk.11,12

Although most pediatric surgeons still favor repair of in-guinal hernias in premature neonates before NICU discharge,there has been a movement toward delayed repair.9,13 On thebasis of a comparison of national survey responses, 63% ofpediatric surgeons preferred repair of reducible inguinal her-nia in extremely low birth weight premature neonates beforeNICU discharge in 2005, compared with 71% of pediatricsurgeons in 1993.9,13 In this study, only 56% of premature ne-onates with a diagnosis of inguinal hernia underwent repairbefore discharge, which is compatible with the practice pat-terns reported in the recent survey. No well-designed pro-spective studies have directly compared the benefits andrisks of in-hospital repair versus subsequent outpatient re-pair. However, mounting evidence suggests that incarcera-tion is more frequent in the general population of infants(<1 year of age, including former premature infants) with in-guinal hernia than in neonates who undergo repair duringthe initial hospitalization. Incarceration has been reportedto occur in 15% to 35% of all infants <1 year of age with in-guinal hernia, including 27% in this study.14,15 This rate maybe lower when incarceration is strictly defined as the need forsedation to reduce the hernia.7 By contrast, the rate of ingui-nal hernia in premature neonates who undergo surgery dur-ing their initial hospitalization ranges from 8% to 16%,including 16% in this study.4,6

Avoiding incarceration is the primary motivation forconsidering early surgery in this population. A history of in-carceration is widely reported to increase the risk of subse-quent testicular atrophy and may predispose the child torecurrence.2,4,5 Although rare, incarceration may also causestrangulation with ischemia of the bowel, testicle, or ovary.6

Furthermore, repeat incarceration is postulated to increaseadhesions and scarring, making subsequent repair longerand more technically challenging.6 All else being equal,avoiding episodes of incarceration is clearly advantageous.

Several experts have suggested that repair should beperformed earlier than at NICU discharge when medicallyfeasible.6,10 In a comparison of premature neonates who un-derwent surgery within 1 week of diagnosis or >1 week afterdiagnosis, Vaos et al reported a higher rate of incarcerationwith delayed repair (12% versus 56%).10 The rates of herniarecurrence and testicular atrophy were likewise higher in the

576

group that underwent delayed repair, and the occurrence ofpostoperative apnea was equivalent. In contrast, Gonzalez-Santacruz et al reported no increase in incarceration episodesor testicular atrophy when inguinal hernia repair was delayeduntil NICU discharge.4 Our study supports the assertion thatin a select subset of neonates hospitalized after 40 weeks post-conceptual age, repairing the inguinal hernia earlier than atthe time of NICU discharge may decrease the rate of incarcer-ation.Concern about postoperative respiratory complications,

including apnea events and re-intubation often motivatethe delay of repair until the baby is ready for discharge. Re-spiratory complications have been reported to occur in asmany as 43% of premature neonates undergoing hernia re-pair, with lower weight at surgery and a history of respiratorydistress syndrome being independent risk factors.3 Otherstudies, in contrast, have suggested that early hernia repairactually has a beneficial effect for decreasing oxygen require-ments and improving respiratory function.16 All studies ofpostoperative respiratory complications have been retrospec-tive, with small numbers of patients from single institutions.Further data are needed to understand the true, current riskof respiratory complications and the association with gesta-tional age, birth weight, age, and size at surgery.Technical challenges are a major concern when operating

on extremely small neonates. Surgical precision is requiredto avoid damaging the spermatic cord or the hernia sac. Da-vies et al reported an increased rate of complications, includ-ing recurrence, testicular atrophy and hydrocele in infants <3kg undergoing hernia repair.2 The potential for increasedsurgical and respiratory complications, coupled with reportsof equivalent incarceration and testicular atrophy risk, moti-vates surgeons who favor delaying repair until expected dis-charge.1,4 Clinically meaningful endpoints, such as testicularatrophy, respiratory complications, and hernia recurrence,were not evaluated in this study because of the lack oflong-term follow-up in the KID.There are additional inherent limitations to the use of ad-

ministrative data sets. Diagnoses are based on billing data andmay overestimate the rate of incarceration depending on thedefinition used.7 Likewise, the time from birth until herniarepair is based on the date when the hernia repair procedureis coded. There is no guarantee that the procedure was codedon the exact day it was performed. Similarly, the post-conceptual age at the time of surgery was calculated withthe gestational age at birth, which is coded in 2-week inter-vals. The lowest gestational age in the coded range wasused in the calculations. Therefore, the finding of an increasein incarceration risk after 40 weeks post-conceptual age mayactually occur at anywhere from 40 to 42 weeks post-conceptual age. However, overall conclusions supportingearly repair remain unchanged with this 2-week margin forerror.A definitive recommendation cannot be made from this

data set, which lacks details on important early (injury tothe vas deferens or testicular vessels, and need for prolongedpostoperative ventilation) and late (testicular atrophy and

Lautz, Raval, and Reynolds

April 2011 ORIGINAL ARTICLES

hernia recurrence) complications. However, this nationallyrepresentative data set provides support for the widespreadpractice of repairing inguinal hernias in premature infantsbefore hospital discharge. It further suggests that special con-sideration should be given to neonates who remain hospital-ized after 40 weeks post-conceptual age. As permitted by theirco-morbid conditions, these infants may benefit from earlierrepair to avoid unnecessarily increasing their risk of incarcer-ation. n

Submitted for publication Jun 29, 2010; last revision received Aug 16, 2010;

accepted Sep 20, 2010.

Reprint requests: Marleta Reynolds, MD, 2300 Children’s Plaza, Box 63,

Chicago, IL 60614. E-mail: MReynolds@childrensmemorial.org

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