Objectives. There have been many recent reports of improved survival rates for congenital diaphragmatic hernia ( CDH), largely derived from institution-based data. These are often flawed by case selection bias. The objectives of this study were to document the true incidence, management, and outcomes of CDH in a geographically defined population over a 12- year period and to determine the changing trends in these over time. We also sought to ascertain the prenatal and postnatal factors associated with morbidity and death among these infants.Methods. A retrospective study of all cases of CDH in Western Australia from 1991 to 2002 was conducted. Cases were identified from 5 independent databases within the Western Australian health network, including the Western Australian Birth Defects Registry. All fetuses and neonates diagnosed with CDH in Western Australia during this period were identified, including miscarriages, stillbirths, and terminations of pregnancies in which a diagnosis of fetal CDH had been made, as well as those diagnosed postnatally. Cases not known to involve CDH until diagnosis at autopsy were also included. Infants with diaphragmatic eventration were excluded from the study. Detailed information was obtained from review of maternal and infant medical records.Results. One hundred sixteen cases of CDH were identified. Of these, 71 ( 61%) infants were born alive and 37 survived beyond 1 year of age ( 52% of live- born infants, 32% of all cases of CDH). Pregnancies involving 38 ( 33%) fetuses were terminated electively, 4 ( 3%) fetuses were aborted spontaneously, and 3 ( 3%) fetuses were stillborn. Another major congenital anomaly was present in 54 ( 47%) cases. Twenty- one ( 18%) cases had other anomalies that were likely to be fatal. Of all cases with an additional major anomaly, 42 ( 78%) died. Twenty- seven ( 71%) of 38 fetuses for whom the pregnancy was terminated had another major anomaly. Twenty- three ( 32%) live- born infants had another major anomaly ( 4 of which were considered fatal conditions); however, this did not affect their survival rates. Fifty- three percent of cases were diagnosed prenatally, and 49% of these pregnancies were then terminated. Of live- born infants with prenatally diagnosed CDH, 10 ( 33%) survived beyond 1 year of age. The gestational age at diagnosis did not affect the survival rate for live- born infants. Postnatal diagnosis occurred in 55 ( 47%) cases. Of these, 41 ( 74%) case subjects were born alive and diagnosed on clinical grounds after birth. In the remaining 14 cases, the diagnosis was made in postmortem examinations of fetuses from pregnancies that were terminated for other reasons ( 8 cases) or after spontaneous abortion or stillbirth ( 5 cases). Significant differences were found between prenatally and postnatally diagnosed live- born infants. Among live- born infants, prenatal diagnosis was associated with a significantly reduced survival rate ( 33%, compared with 66% for postnatally diagnosed infants). Prenatally diagnosed live- born infants were of lower birth weight and were born at an earlier gestational age. There was no statistically significant difference between the 2 groups in the onset of labor ( spontaneous or induced) or in the rate of elective cesarean sections. Prenatally diagnosed live- born infants were more likely to be delivered in a tertiary perinatal center and were intubated more commonly at delivery. No difference was found in the Apgar scores at either 1 or 5 minutes between the groups. Of 71 live- born infants, 37 ( 52%) survived to 1 year of age. The majority of deaths occurred within the first 7 days of life ( 44%). Preoperative air leaks occurred for 16 ( 22%) infants, of whom 14 ( 88%) died. Factors found to predict death of live- born infants included prenatal diagnosis, right- sided hernia, major air leak, earlier gestational age at birth, lower birth weight, and lower Apgar scores at 1 and 5 minutes. Over the course of the decade, there were significant increases in the proportion of cases in which the diagnosis of CDH was made with prenatal ultrasonography and in the number of live- born infants born at the tertiary perinatal center. The mortality rate for all cases, the mortality rate for live- born infants, and the proportion of pregnancies involving prenatally diagnosed cases that were terminated electively were all greater in the later epoch but not significantly so.Conclusions. This was a comprehensive, population-based study of CDH, with full case ascertainment, large sample size, and complete outcome data for all cases. The majority of published studies of CDH examined specific patient populations, such as neonates referred to tertiary pediatric surgical centers. Invariably, those studies failed to detect the demise of cases with CDH before arrival at the referral center, whether through termination of pregnancy, in utero fetal demise, or postnatal death occurring before transfer. Exclusion of these cases from calculations of mortality rates results in significant case selection bias. In our study, 35% of live- born infants died before referral or transport. The population of infants reaching the tertiary surgical center represented only 40% of the total cases of CDH. Wide variations in reported survival rates occur throughout the literature. These differences reflect the influence of this case selection bias, as well as variable referral policies and management practices. For our study population, survival rates differed vastly depending on the subgroup analyzed. Ninety- two percent of postoperative infants survived beyond 1 year of age, as did 80% of infants who reached the surgical referral center. However, only 52% of live- born infants, 32% of all cases, and 16% of all prenatally diagnosed cases survived. Therefore, the overall mortality rate for this condition remains high, despite increased prenatal detection, transfer to tertiary institutions for delivery, and advances in neonatal care, and is influenced significantly by the rate of prenatal termination. In our study, 33% of all cases of CDH and 49% of prenatally diagnosed fetuses underwent elective termination of pregnancy. This large number of fetal terminations confounds the accurate assessment of the true outcomes of this condition.