We observed a consistent rise in IVH incidence over the past decade, despite a decrease in mortality among VLBW infants. Notably, both short-term outcomes (such as BPD and ROP) and long-term outcomes (including CP and seizure disorder) have shown improvement over this period in VLBW infants with IVH. However, among infants with IVH who underwent surgical treatment (10%), there was a tendency towards more severe co-morbidities and long-term sequelae, such as CP, DD, and seizure disorder. Additionally, these infants exhibited a higher prevalence of growth below the 10th percentile in HT, WT, and HC, as well as poorer developmental test results, compared with those without treatment. It is noteworthy that significant improvements were observed when dividing the study period into two halves of 4 years each. This study, encompassing almost all infants, as per information from the Korean Statistical Information Service, provides valuable insights into the nationwide epidemiology of IVH over the past decade.

Advancements in neonatal intensive care have led to improved survival rates for extremely preterm infants [23]. Stoll et al. argued that the effort to save more high-risk infants has resulted in an increased proportion of IVH. They reported that the decreasing trend of IVH rates, which reached 14% in 2002, either stabilized or showed a relative increase, reaching 16% in 2007 [5, 6]. The global incidence range of IVH G3 and G4 was reported to be 6%–22%, with variations by region (Europe: 6%–17%; North America: 11%–22%; Asia: 10%–14%; Oceania: 12%–13%) [14]. IVH G2 had an incidence range of 5%–19%. Among infants with a gestational age of less than 24 weeks, the incidence of IVH was close to 37%. Generally, the incidence of IVH was inversely related to gestational age. In our cohort, the overall prevalence of IVH (≥ G2) in VLBW infants was 12.1%. It is worth noting that Stoll et al. observed increasing trends in both BPD and IVH, whereas our cohort exhibited a decreasing trend in BPD [5]. This disparity may be attributed to the fact that their measurements were taken from a slightly earlier era, during which ventilator strategies for BPD and post-natal corticosteroid administration have evolved over the past decade [24, 25].

IVH is closely linked to increased mortality and neurodevelopmental abnormalities. Notably, neonates with IVH G3 and G4 are at high risk of experiencing long-term neurologic and neurodevelopmental disabilities, including seizures, cognitive and executive function impairment, and CP [2,3,4]. In Korea, the mortality rate among VLBW infants stood at approximately 20%, with IVH-related mortality accounting for 7% of this total. Subsequent follow-up studies, conducted until the age of 22, unveiled those individuals with IVH faced a 4.2-fold increased risk of developing CP [11]. Furthermore, the risk of cardiovascular, respiratory, digestive, eye and ear issues, as well as malignant tumors, continued to rise, leading to a lifelong burden for patients [26,27,28]. IVH patients exhibited a 2.68-fold increased risk of having an intelligence quotient (IQ) below 2 SD, a 4.45-fold increased risk of motor dysfunction, and a 2.91-fold increased risk of encountering difficulties in any academic skills (below 2 SD) [29,30,31]. In this study, CP was diagnosed in 837 patients with IVH (28%), and DD was observed in 1095 patients (36%). While it is about known that CP occurs in about 20–30% of cases after IVH, long-term outcomes following ventricular drainage have not been extensively studied [32]. The data from a single-center cohort revealed that the mortality rate of IVH was 36.9%. Among the 77 surviving patients, the rate of surgical treatment after PHVD was 18%, and the incidence of CP was 55.9% (49.4%) [33].

In some cases, infants who are unable to tolerate a permanent shunt due to specific conditions may undergo a temporizing surgical procedure to divert cerebrospinal fluid until these issues are resolved. Published rates of conversion from a temporary device to a permanent shunt in this population vary, ranging from just over 50% to as high as 85% [16, 17, 34,35,36]. In 2019, the Early Versus Late Intervention Study (ELVIS) Trial group in the Netherlands demonstrated the highest recorded conversion rate, at 26% [37, 38]. In this study, temporary devices were used in 1.2% of IVH VLBW infants, while permanent shunts were required in 4.8% of cases. The conversion rate from temporary to permanent devices was 42.3%.

Notably, the risk of a poor neurodevelopmental outcome is significantly higher when severe IVH is complicated by PHVD, with a prevalence ranging from 40 to 60%. Further risk is observed in infants who eventually require a shunt, with prevalence as high as 75% to 88% [14, 15]. In the pre-surfactant era, up to 82% of infants with PHVD who survived developed significant neurologic impairments, including CP [39]. In our study, CP was reported in 245 patients (76%) in the surgical intervention group, which was higher than the 77 patients (24%) in the non-surgical intervention group.

In our study, the K-DST identified 16 patients (12.8%) categorized as requiring “further work-up”. When dividing the study period into the first half and the more recent half, the percentage was 12.7% from 2010 to 2013 and 11.3% from 2014 to 2017. These findings suggest that improved neonatal care and high-risk infant follow-up care have led to a significant reduction in abnormal neurodevelopmental results. However, among patients who underwent surgical treatment, the percentage of those categorized as “further work-up” was 13%, compared with 11% of infants without treatment. This highlights the need for careful consideration and early intervention in such cases.

This study boasts several strengths, notably its nationwide scope, enabling a comprehensive epidemiological analysis of IVH and PHVD in VLBW infants across all live births. Additionally, the analysis included long-term growth and developmental screening data until the age of six years.

However, it is crucial to acknowledge certain limitations in this study. Due to the nature of national health claim data, access to individual patient data was not possible. The study design was observational, and patient inclusion relied solely on ICD-10 codes, which may have introduced labeling errors or missed diagnoses from various hospitals that could not be rectified. The surgically treated group can be considered as having PHVD; however, it is important to note that treatment approaches vary among different institutes, introducing an additional challenge in drawing conclusive findings. We can only make assumptions that patients who receive surgical treatment might represent a more complex spectrum of the disease. Controlling for the heterogeneity and subjectivity in measuring scales across various units and clinicians was not feasible in this retrospective observational study. Furthermore, recent studies have proposed distinct outcomes associated with periventricular hemorrhagic infarction, suggesting the implication of different etiologies, as described by Volpe et al., rather than the traditional description by Papile et al. [4, 39, 40]. The diagnosis was applied according to the ICD-10 code inputted by the hospital. It was not possible to distinguish which diagnostic criteria were used between the Papile and Volpe criteria. To further enhance our understanding, future data collection efforts should categorize cases according to the provided diagnostic classification. While the K-DST was used as a developmental screening tool, the Bayley Scales of Infant Development were not employed as a diagnostic tool. Additionally, the study did not assess the association between outborn birth status and mortality or morbidity. Lastly, the duration of follow-up data was relatively short, potentially leading to an underestimation of developmental disorders that typically manifest after the age of three.

In conclusion, despite advancements in current neonatal care, the neurodevelopmental outcomes of infants with IVH, especially those who undergo surgical treatment, continue to be a matter of concern. It is imperative to prioritize specialized care for patients receiving surgical treatment and closely monitor their growth and development after discharge to improve developmental prognosis.