Joint reaction and simulated muscle forces during squatting and walking in persons with hemophilia.

BACKGROUND: Persons with hemophilia experience joint bleeding that can lead to debilitating arthropathy, most commonly seen in ankles, knees, and elbows. Arthropathy can hinder participation in daily and athletic activities. We explored how hemophilic arthropathy impacts movement patterns in walking and bilateral squatting tasks in persons with hemophilia compared to healthy controls. METHODS: Persons with hemophilia and healthy controls completed walking and squatting tasks while kinematic and kinetic motion capture data were collected. The Hemophilia Joint Health Score exam was performed to measure hemophiliac arthropathy. OpenSim was used to model muscle and joint reaction forces and calculate moments and angles. Peak values were compared using Cohen's d to estimate effect sizes of hemophilia on movement parameters. FINDINGS: Nine persons with hemophilia and eight age-matched controls were analyzed. Temporal-spatial metrics were similar between hemophilia and control groups in both tasks. In walking, persons with hemophilia had higher peak ankle dorsiflexion angles, vertical ground reaction force weight acceptance peaks, and hip extension and flexion moments compared to controls. In squatting, persons with hemophilia had lower knee extension moments, ankle joint reaction force, and knee extensor forces, but had higher hip extension moments. INTERPRETATION: Temporal-spatial metric similarity between hemophilia and controls suggests that kinetic and kinematic analyses are needed to identify movement pattern differences. These data identify potential compensatory strategies at the hip that may be used by persons with hemophilia to mitigate impact on the knee and ankle. Future work will confirm these data in a larger sample size and be used to develop physical therapy strategies.

Duration of Anticoagulation for Venous Thromboembolism in Pediatric Patients: Kids-DOTT Trial Outcomes at Two Years.

BACKGROUND: The Kids-DOTT multinational randomized clinical trial (RCT) revealed non-inferiority of a six-week versus three-month duration of anticoagulation for the treatment of provoked venous thromboembolism (VTE) in patients <21 years old, in regard to net clinical benefit at one year. OBJECTIVE: To evaluate non-inferiority at two years. PATIENTS/METHODS: Patients whose repeat imaging six weeks after VTE diagnosis did not show complete veno-occlusion were randomized to discontinue anticoagulation versus receive a total three-month course and followed for two years for the occurrence of symptomatic recurrent (SR-) VTE (efficacy outcome) and clinically-relevant bleeding (CRB, safety outcome). Outcomes were centrally adjudicated and net clinical benefit was compared between treatment arms via a pre-specified bivariate non-inferiority boundary, using 95% confidence intervals (CIs) in absolute risk differences (ARDs) between treatment arms. RESULTS: Kaplan-Meier estimates of two-year cumulative incidences in the six-week and three-months arms of the intention-to-treat (ITT) population (n=417) were 1.7% (95% CI: 0%, 3.7%) and 2.9% (95% CI: 0.3%, 5.4%) for SR-VTE and 1.1% (95% CI: 0%, 2.5%) and 3.2% (95% CI: 0.6%, 5.7%) for CRB. Bivariate analysis of the ARDs in the ITT population demonstrated that a six-week anticoagulation duration was non-inferior to a three-month course. CONCLUSIONS: These findings support durability of the Kids-DOTT RCT findings of net clinical benefit at two years.

Anticoagulation in Pediatric Patients.

The use of antithrombotic agents is increasing in infants, children and adolescents. The more recent routine inclusion of children in FDA-monitored clinical trials has propelled the rapid accumulation of safety and efficacy data on these agents in pediatric patients. Antithrombotic agents in current use include indirect or antithrombin-dependent anticoagulants, intravenous direct thrombin inhibitors, direct oral anticoagulants (DOACs) targeting thrombin or factor Xa, antiplatelet agents and thrombolytic therapies. Each class of antithrombotic agent has distinct mechanisms of action, clearance routes, half-lives, safety and dosing. Anticoagulant efficacy is dependent upon the specific clinical indication and stability of the pediatric patient. Duration of anticoagulant course is also dependent upon the clinical indication as well as rate of thrombus resolution. This manuscript reviews the mechanism of action, route of administration, route of clearance and plasma half-life for the antithrombotic agents in current use in children. Use of anticoagulation in the context of thrombolytic therapy is discussed.

Management of pregnancy and delivery in congenital fibrinogen disorders: communication from the ISTH SSC Subcommittee on Factor XIII and Fibrinogen.

Congenital fibrinogen disorders (CFDs) are a heterogeneous group of rare congenital quantitative and/or qualitative fibrinogen deficiencies. The spectrum of molecular anomalies is broad, leading to several subtypes of fibrinogen disorders (ie, afibrinogenemia, hypofibrinogenemia, dysfibrinogenemia, and hypodysfibrinogenemia). Pregnancy in women with CFDs is a high-risk clinical situation, with an increased tendency for miscarriages, bleeding, and thrombosis. Even though it is well established that management of such pregnancies requires a multidisciplinary approach involving specialists (hematologists and maternal/fetal medicine experts with expertise in the management of inherited bleeding disorders), specific guidelines are lacking. In this International Society on Thrombosis and Haemostasis (ISTH) Scientific and Standardization Committee communication, we aim to propose an expert consensus opinion with literature evidence where available on the strategy for management of pregnancy, delivery, and puerperium in CFDs.

Hemostasis in the Pregnant Woman, the Placenta, the Fetus, and the Newborn Infant.

The hemostasis system is composed of procoagulant, anticoagulant, and fibrinolytic proteins that interact with endothelial and blood cells and with each other in a complex system of checks and balances to maintain blood flow while preventing both hemorrhage and thrombosis. Pregnancy is a unique physiological state in which biological alterations predispose both mother and fetus to both bleeding and clotting. The placenta is a vascular interface for maternal and fetal blood exchange which predisposes the mother to hemorrhage. Maternal hemostasis presents a compensatory hypercoagulability including elevated factor VIII, von Willebrand factor, fibrinogen and thrombin generation, decreased thrombin regulation with resistance to activated protein C and decreased free protein S, and decreased fibrinolysis with increased plasminogen activator inhibitors. The placental vascular surface is of fetal trophoblastic origin that derives many characteristics of endothelium but differs in that tissue factor is constitutively expressed. Ontogeny of fetal hemostasis is characteristic. Platelets, von Willebrand factor, factor VIII, and fibrinogen are expressed and mature early in gestation, while vitamin K-dependent and contact factors exhibit delayed development. The fetal hemostatic system has a decreased capacity to generate or regulate thrombin, resulting in a fragile balance with little capacity to compensate under stress conditions, particularly in the infant born prematurely. Dysfunction of the maternal/placental/fetal unit gives rise to gestational disorders including preeclampsia, fetal growth restriction, placental abruption, and premature delivery. Knowledge of normal hemostasis levels and function are critical to evaluate bleeding or clotting syndromes in the pregnant woman and her fetus or newborn infant.

Effect of Anticoagulant Therapy for 6 Weeks vs 3 Months on Recurrence and Bleeding Events in Patients Younger Than 21 Years of Age With Provoked Venous Thromboembolism: The Kids-DOTT Randomized Clinical Trial.

Importance: Among patients younger than 21 years of age, the optimal duration of anticoagulant therapy for venous thromboembolism is unknown. Objective: To test the hypothesis that a 6-week duration of anticoagulant therapy for provoked venous thromboembolism is noninferior to a conventional 3-month therapy duration in patients younger than 21 years of age. Design, Setting, and Participants: Randomized clinical trial involving 417 patients younger than 21 years of age with acute, provoked venous thromboembolism enrolled at 42 centers in 5 countries from 2008-2021. The main exclusions were severe anticoagulant deficiencies or prior venous thromboembolism. Patients without persistent antiphospholipid antibodies and whose thrombi were resolved or not completely occlusive upon repeat imaging at 6 weeks after diagnosis underwent randomization. The final visit for the primary end points occurred in January 2021. Interventions: Total duration for anticoagulant therapy of 6 weeks (n = 207) vs 3 months (n = 210) for provoked venous thromboembolism. Main Outcomes and Measures: The primary efficacy and safety end points were centrally adjudicated symptomatic recurrent venous thromboembolism and clinically relevant bleeding events within 1 year blinded to treatment group. The primary analysis was noninferiority in the per-protocol population. The noninferiority boundary incorporated a bivariate trade-off that included an absolute increase of 0% in symptomatic recurrent venous thromboembolism with an absolute risk reduction of 4% in clinically relevant bleeding events (1 of 3 points on the bivariate noninferiority boundary curve). Results: Among 417 randomized patients, 297 (median age, 8.3 [range, 0.04-20.9] years; 49% female) met criteria for the primary per-protocol population analysis. The Kaplan-Meier estimate for the 1-year cumulative incidence of the primary efficacy outcome was 0.66% (95% CI, 0%-1.95%) in the 6-week anticoagulant therapy group and 0.70% (95% CI, 0%-2.07%) in the 3-month anticoagulant therapy group, and for the primary safety outcome, the incidence was 0.65% (95% CI, 0%-1.91%) and 0.70% (95% CI, 0%-2.06%). Based on absolute risk differences in recurrent venous thromboembolism and clinically relevant bleeding events between groups, noninferiority was demonstrated. Adverse events occurred in 26% of patients in the 6-week anticoagulant therapy group and in 32% of patients in the 3-month anticoagulant therapy group; the most common adverse event was fever (1.9% and 3.4%, respectively). Conclusions and Relevance: Among patients younger than 21 years of age with provoked venous thromboembolism, anticoagulant therapy for 6 weeks compared with 3 months met noninferiority criteria based on the trade-off between recurrent venous thromboembolism risk and bleeding risk. Trial Registration: ClinicalTrials.gov Identifier: NCT00687882.

Outcome measures in Haemophilia: Beyond ABR (Annualized Bleeding Rate).

Options for management of haemophilia are increasing rapidly with completely novel therapeutic approaches that cannot be compared using traditional factor assays. In addition, as prophylaxis regimens have improved, bleeding rates have decreased, and consequently, it is difficult to show an impact of novel therapies on rates of spontaneous bleeding. There is currently an urgent need for a panel of outcome measures to compare therapies that are dissimilar in many essential ways. Conventional objective outcome measures including joint physical examination and joint imaging continue to hold a central importance. Factor assays are essential for evaluation of products derived from native factor genes, but are not applicable to some extended half-life factors or non-factor bypassing agents. Global assays including thrombin generation and chromogenic assays of factor X activation are under investigation for their usefulness in haemophilia assessment. Bleeding rate is a conventional subjective patient-reported outcome that, while decreasing in frequency, is indispensable as an outcome given that the primary manifestation of haemophilia is bleeding. Other patient-reported outcomes such as pain intensity and interference, health-related quality of life and activities and participation are increasingly important to distinguish superior outcomes in comparative trials. This review of outcome measures for haemophilia presents examples of existing outcome measures with an emphasis on their strengths and limitations.

Disseminated Intravascular Coagulation Is an Independent Predictor of Adverse Outcomes in Children in the Emergency Department with Suspected Sepsis.

OBJECTIVE: To evaluate the impact of early disseminated intravascular coagulation (DIC) on illness severity in children using a database of emergency department ED encounters for children with suspected sepsis, in view of similar associations in adults. STUDY DESIGN: Laboratory and clinical data were extracted from a registry of emergency department encounters of children with suspected sepsis between April 1, 2012, and June 26, 2017. International Society of Thrombosis and Hemostasis DIC scores were calculated from laboratory values obtained within 24 hours of emergency department admission. Univariate logistic regression, multivariable logistic regression, and Cox regression were used to assess the influence of DIC scores on vasopressor use (primary outcome), mortality, ventilator requirement, pediatric intensive care unit admission, and hospital duration (secondary outcomes). The optimal DIC score cutoff for outcome prediction was determined. RESULTS: Of 1653 eligible patients, 284 had DIC scores within 24 hours, including 92 who required vasopressors and 23 who died within 1 year. An initial DIC score of ≥3 was the most sensitive and specific DIC score for predicting adverse outcomes. Those with a DIC score of ≥3 vs <3 had increased odds of vasopressor use in both univariate (OR, 4.48; 95% CI, 2.63-7.62; P < .001) and multivariable (OR, 3.78; 95% CI, 1.82-7.85; P < .001) analyses. Additionally, those with a DIC score of ≥3 vs <3 had increased 1-year mortality with a hazard ratio of 3.55 (95% CI, 1.46-8.64; P = .005). CONCLUSIONS: A DIC score of ≥3 was an independent predictor for both vasopressor use and mortality in this pediatric cohort, distinct from the adult overt DIC score cutoff of ≥5.

Young adult outcomes of childhood prophylaxis for severe hemophilia A: results of the Joint Outcome Continuation Study.

The Joint Outcome Study (JOS), a randomized controlled trial, demonstrated that children with severe hemophilia A (HA) initiating prophylactic factor VIII (FVIII) prior to age 2.5 years had reduced joint damage at age 6 years compared with those treated with episodic FVIII for bleeding. The Joint Outcome Continuation Study (JOS-C) evaluated early vs delayed prophylaxis effects on long-term joint health, following JOS participants to age 18 years in an observational, partially retrospective study. Index joint magnetic resonance imaging (MRI) scores of osteochondral (OC) damage (primary outcome), joint physical examination scores, and annualized rates of joint/other bleeding episodes (secondary outcomes) were collected. Thirty-seven of 65 JOS participants enrolled in JOS-C, including 15 randomized to prophylaxis at mean age 1.3 years ("early prophylaxis"); 18 initially randomized to episodic treatment, starting "delayed prophylaxis" at mean age 7.5 years; and 4 with high-titer inhibitors. At JOS-C exit, MRI OC damage was found in 77% of those on delayed and 35% of those on early prophylaxis for an odds ratio of OC damage, in the delayed vs early prophylaxis group, of 6.3 (95% confidence interval, 1.3, 29.9; P = .02). Annualized bleeding rates were higher with delayed prophylaxis (mean plus or minus standard deviation, 10.6 ± 6.6 vs 3.5 ± 2.1; P < .001), including when only comparing time periods on prophylaxis (6.2 ± 5.3 vs 3.3 ± 1.9; P < .05). In severe HA, early initiation of prophylaxis provided continued protection against joint damage throughout childhood compared with delayed initiation, but early prophylaxis was not sufficient to fully prevent damage. This trial was registered at www.clinicaltrials.gov as #NCT01000844.

A mathematical model of coagulation under flow identifies factor V as a modifier of thrombin generation in hemophilia A.

BACKGROUND: The variability in bleeding patterns among individuals with hemophilia A, who have similar factor VIII (FVIII) levels, is significant and the origins are unknown. OBJECTIVE: To use a previously validated mathematical model of flow-mediated coagulation as a screening tool to identify parameters that are most likely to enhance thrombin generation in the context of FVIII deficiency. METHODS: We performed a global sensitivity analysis (GSA) on our mathematical model to identify potential modifiers of thrombin generation. Candidates from the GSA were confirmed by calibrated automated thrombography (CAT) and flow assays on collagen-tissue factor (TF) surfaces at a shear rate of 100 per second. RESULTS: Simulations identified low-normal factor V (FV) (50%) as the strongest modifier, with additional thrombin enhancement when combined with high-normal prothrombin (150%). Low-normal FV levels or partial FV inhibition (60% activity) augmented thrombin generation in FVIII-inhibited or FVIII-deficient plasma in CAT. Partial FV inhibition (60%) boosted fibrin deposition in flow assays performed with whole blood from individuals with mild and moderate FVIII deficiencies. These effects were amplified by high-normal prothrombin levels in both experimental models. CONCLUSIONS: These results show that low-normal FV levels can enhance thrombin generation in hemophilia A. Further explorations with the mathematical model suggest a potential mechanism: lowering FV reduces competition between FV and FVIII for factor Xa (FXa) on activated platelet surfaces (APS), which enhances FVIII activation and rescues thrombin generation in FVIII-deficient blood.

Validity and reliability of the Colorado Adult Joint Assessment Scale in adults with moderate-severe hemophilia A.

BACKGROUND: The Colorado Adult Joint Assessment Scale (CAJAS) is designed to assess joint health in adults with hemophilia. The CAJAS comprises nine items (swelling, muscle atrophy, axial deformity, crepitus, range of motion, contracture, instability, strength, gait) and assesses six joints. OBJECTIVE: To assess CAJAS content validity and psychometric properties. PATIENTS/METHODS: Data were obtained from the Trial to Evaluate the Effect of Secondary Prophylaxis With rFVIII Therapy in Severe Hemophilia A Adult and/or Adolescent Subjects Compared to That of Episodic Treatment (SPINART) study and a separate CAJAS validation study. CAJAS assessments in SPINART were performed by physical therapists (PTs) from the United States, Romania, Bulgaria, and Argentina. In the validation study, content validity was assessed from interviews with six PTs at three US hemophilia centers; cultural equivalence was assessed with seven non-US PTs from SPINART. Reliability data were collected from 30 subjects at four US centers. Test-retest reliability was evaluated by having the same PT perform CAJAS examinations at two visits, 7-10 days apart. Inter-rater reliability was assessed by comparing CAJAS scores of two different PTs performing separate examinations of the same patient several hours apart at the same visit. Psychometric properties were assessed using SPINART and validation study data. RESULTS: The CAJAS demonstrated good content validity. Test-retest reliability was high (intraclass correlation coefficient, 0.98), as was inter-rater reliability (intraclass correlation coefficient, 0.88). Internal consistency reliability was strong (α = .90). The CAJAS demonstrated good convergent/divergent validity, known-groups validity, and ability to detect change. CONCLUSIONS: The CAJAS is a valid and reliable measure of joint health in adults with moderate-severe hemophilia and is appropriate for use in clinical practice.

Factor VIII prophylaxis effects outweigh other hemostasis contributors in predicting severe haemophilia A joint outcomes.

INTRODUCTION: The Joint Outcome Study (JOS) demonstrated that previously untreated children with severe haemophilia A treated with prophylactic factor VIII (FVIII) concentrate had superior joint outcomes at age 6 years compared to those children treated episodically for bleeding. However, variation in joint outcome within each treatment arm was not well explained. AIM: In this study, we sought to better understand variation in joint outcomes at age 6 years in participants of the JOS. METHODS: We evaluated the influence of FVIII half-life, treatment adherence, constitutional coagulant and anticoagulant proteins, and global assays on joint outcomes (number of joint bleeds, total number of bleeds, total MRI score and joint physical exam score). Logistic regression was used to evaluate the association of variables with joint failure status on MRI, defined as presence of subchondral cyst, surface erosion or joint-space narrowing. Each parameter was also correlated with each joint outcome using Spearman correlations. RESULTS: Prophylaxis treatment arm and FVIII trough were each found to reduce risk of joint failure on univariate logistic regression analysis. When controlling for treatment arm, FVIII trough was no longer significant, likely because of the high level of covariation between these variables. We found no consistent correlation between any laboratory assay performed and any joint outcome parameter measured. CONCLUSION: In the JOS, the effect of prescribed prophylactic FVIII infusions on joint outcome overshadowed the contribution of treatment adherence, FVIII half-life, global assays of coagulation and constitutional coagulation proteins. (ClinicalTrials.gov number, NCT00207597).

Effects of anti-ß2GPI antibodies on VWF release from human umbilical vein endothelial cells and ADAMTS13 activity.

BACKGROUND: Antiphospholipid syndrome (APS) is characterized by recurrent thromboembolic events in the setting of pathologic autoantibodies, some of which are directed to ß2-Glycoprotein 1 (ß2GPI). The mechanisms of thrombosis in APS appear to be multifactorial and likely include a component of endothelial activation. Among other things, activated endothelium secretes von Willebrand factor, a hemostatic protein that in excess can increase the risk of thrombosis. OBJECTIVE: We hypothesized that anti-ß2GPI antibodies could regulate the release and modulation of VWF from endothelial cells. PATIENTS/METHODS: Isolated anti-ß2GPI antibodies from patients with APS were assayed for their ability to induced VWF release from HUVECs and modulate the effects of ADAMTS13 in a shear-dependent assay. RESULTS: We observed that anti-ß2GPI antibodies from some patients with APS induced VWF release from human endothelial cells but did not induce formation of cell-anchored VWF-platelet strings. Finally, we also determined that one of the Anti-ß2GPI antibodies tested can inhibit the function of ADAMTS13, the main modulator of extracellular VWF. CONCLUSIONS: These results suggest that VWF and ADAMTS13 may play a role in the prothrombotic phenotype of APS.

A cross-sectional analysis of cardiovascular disease in the hemophilia population.

Men with hemophilia were initially thought to be protected from cardiovascular disease (CVD), but it is now clear that atherothrombotic events occur. The primary objective of the CVD in Hemophilia study was to determine the prevalence of CVD and CVD risk factors in US older men with moderate and severe hemophilia and to compare findings with those reported in age-comparable men in the Atherosclerosis Risk in Communities (ARIC) cohort. We hypothesized if lower factor levels are protective from CVD, we would see a difference in CVD rates between more severely affected and unaffected men. Beginning in October 2012, 200 patients with moderate or severe hemophilia A or B (factor VIII or IX level ≤ 5%), aged 54 to 73 years, were enrolled at 19 US hemophilia treatment centers. Data were collected from patient interview and medical records. A fasting blood sample and electrocardiogram (ECG) were obtained and assayed and read centrally. CVD was defined as any angina, any myocardial infarction by ECG or physician diagnosis, any self-reported nonhemorrhagic stroke or transient ischemic attack verified by physicians, or any history of coronary bypass graft surgery or coronary artery angioplasty. CVD risk factors were common in the population. Compared with men of similar age in the ARIC cohort, patients with hemophilia had significantly less CVD (15% vs 25.8%; P < .001). However, on an individual patient level, CVD events occur and efforts to prevent cardiovascular events are warranted. Few men were receiving secondary prophylaxis with low-dose aspirin, despite published opinion that it can be used safely in this patient population.

Variants in chondroitin sulfate metabolism genes in thrombotic storm.

INTRODUCTION: Thrombotic storm (TS) presents as a severe, acute thrombotic phenotype, characterized by multiple clotting events and frequently affecting younger adults. Understanding the extensive hypercoagulation of an extreme phenotype as TS will also provide insight into the pathogenesis of a wider spectrum of thrombotic disorders. MATERIAL AND METHODS: We completed whole exome sequencing on 26 TS patients, including 1 multiplex family, 13 trios and 12 isolated TS patients. We examined both dominant and recessive inheritance models for known thrombotic factors as well as performed a genome-wide screen. Identified genes of interest in the family and trios were screened in the remaining TS patients. Variants were filtered on frequency (<5% in 1000 genomes), conservation and function in gene and were annotated for effect on protein and overall functionality. RESULTS: We observed an accumulation of variants in genes linked to chondroitin sulfate (CS), but not heparan sulfate metabolism. Sixteen conserved, rare missense and nonsense variants in genes involved in CS metabolism (CHPF, CHPF2, CHST3, CHST12, CHST15, SLC26A2, PAPSS2, STAB2) were identified in over one-third of the TS patients. In contrast, we identified only seven variants in known thrombosis genes (including FV Leiden). CONCLUSIONS: As CS has multiple functions in the glycocalyx protecting the endothelial cells, reduced availability of CS could diminish the normal control mechanisms for blood coagulation, making these CS metabolism genes strong potential risk factors for TS. Overall, no single gene was identified with strong evidence for TS causality; however, our data suggest TS is mediated by an accumulation of rare pro-thrombotic risk factors.

Pediatric Thrombolysis: A Practical Approach.

The incidence of pediatric venous thromboembolic disease is increasing in hospitalized children. While the mainstay of treatment of pediatric thrombosis is anticoagulation, reports on the use of systemic thrombolysis, endovascular thrombolysis, and mechanical thrombectomy have steadily been increasing in this population. Thrombolysis is indicated in the setting of life- or limb-threatening thrombosis. Thrombolysis can rapidly improve venous patency thereby quickly ameliorating acute signs and symptoms of thrombosis and may improve long-term outcomes such as postthrombotic syndrome. Systemic and endovascular thrombolysis can result in an increase in minor bleeding in pediatric patients, compared with anticoagulation alone, and major bleeding events are a continued concern. Also, endovascular treatment is invasive and requires technical expertise by interventional radiology or vascular surgery, and such expertise may be lacking at many pediatric centers. The goal of this mini-review is to summarize the current state of knowledge of thrombolysis/thrombectomy techniques, benefits, and challenges in pediatric thrombosis.

Intracranial haemorrhage in children and adolescents with severe haemophilia A or B - the impact of prophylactic treatment.

The discussion of prophylactic therapy in haemophilia is largely focused on joint outcomes. The impact of prophylactic therapy on intracranial haemorrhage (ICH) is less known. This study aimed to analyse ICH in children with haemophilia, with a focus on different prophylaxis regimens and sequelae of ICH. We conducted a multicentre retrospective and prospective study that included 33 haemophilia centres from 20 countries. Inclusion criteria were children and adolescents born between 1993 and 2014, with severe haemophilia A or B without inhibitors. Participants were categorized by prophylaxis regimen: full, partial or none, based on dose and dose frequency of regular infusions. The cohort study included 1515 children: 29 cases of ICH over 8038 patient years were reported. The incidence of ICH in the prophylaxis group, 0·00033 cases of ICH/patient year, was significantly lower compared to the no prophylaxis group, 0·017 cases of ICH/patient year (RR 50·06; P < 0·001) and the partial prophylaxis group, 0·0050 cases of ICH/patient year (RR 14·92; P = 0·007). In the on-demand-group, 8% (2/24) children with ICH died and 33% had long-term sequelae, including intellectual and behavioural problems, paresis and epilepsy. Children on regular, frequent prophylaxis have a low risk of ICH compared to those using non-frequent or no prophylaxis.