This study longitudinally observes the intergenerational (mother-child) continuum in hemophilia A from pregnancy through early childhood. Because the study follows mother-child pairs, the study includes both a maternal cohort and a pediatric cohort. Each cohort has a primary goal: for the mother with a severe hemophilia genotype, the overarching primary goal is to understand the risks for pregnancy-associated bleeding and postpartum hemorrhage (PPH); for the child, the overarching primary goal is to understand the risks, timing, and circumstances of development of anti-FVIII antibodies. From a longitudinal perspective, risks for both bleeding in the mother and anti-FVIII antibody development in the child are expected to be influenced over time by genetic and environmental factors that begin early in (or before) pregnancy. Enrollment of blood relatives is offered to improve power to better understand inherited contributions to bleeding and inhibitor development in the mother-baby pairs.

HARP is a longitudinal observational, decentralized and multisite (with one hybrid site), national prospective cohort study in hemophilia A. Participants will be treated by their HCPs, with no limitations on medical decision-making.

Hemophilia A is an inherited X-linked bleeding disorder caused by deficiency in coagulation factor VIII (FVIII). Severe hemophilia A is defined by a FVIII level < 0.01 IU/dL (or < 1%). A significant complication of hemophilia A is the development of immune responses to FVIII, also known as inhibitors. In pregnancy, mothers who have a hemophilia-causing genotype are at high-risk for postpartum hemorrhage (PPH). Genetics, other health factors, and environment are all thought to contribute to immune responses and bleeding risks. This study seeks to better understand factors involved in inhibitor development and bleeding beginning before birth.

To accomplish the goal of following 50 mother-child pairs with a child affected by severe hemophilia A from pregnancy through at least the first 2 years of life, we expect to enroll approximately 120 pregnant mothers with a pregnancy at-risk of being affected by severe hemophilia A. The biological father, first- and second-degree blood relatives of the child, and other relatives whose data or samples may be informative for the planned genetic studies of hemophilia and inhibitors may be invited to participate in the study and provide data and samples in order to improve power of the study to robustly investigate the heritable causes of bleeding and inhibitors.

Based on incidence and prevalence calculations of hemophilia by the Centers for Disease Control and Prevention, approximately 150 males are born with severe hemophilia A in the United States annually. Because one-third of these patients should not have a prior family history, a conservative estimate for new babies with severe hemophilia A born into a family known to have hemophilia would be 100 males annually. HARP will open 1-2 U.S. fixed sites, with most participants expected to enroll in the decentralized study.

The HARP study design will enable maternal and neonatal/early life sample and data collection for a continuous picture of hemophilia A phenotypes and immunological development. The duration of participation in HARP for each mother-child pair will be from enrollment during pregnancy until the child is at least 2 years old. Mother-child pairs will complete the study when the child reaches 50 cumulative FVIII EDs without an inhibitor or HARP ends, whichever comes first. The expected range of duration of participation for any one mother-child pair will range from 2.2 years up to 5 years, with many participants expected to be followed for < 3 years.

The primary biological sample type collected in HARP is longitudinal blood samples. Blood samples will be collected at the time of a clinical sample whenever possible to minimize the number of procedures for both mother and child. Leftover clinical blood samples and biological specimens will be used to supplement research samples whenever possible; this will improve the breadth of samples available for research and help to minimize blood volumes taken. Other sources of biological samples (hair, saliva, buccal, urine, stool, cervix, vagina, skin flora, chorionic villus, amniotic fluid, umbilical cord blood, umbilical cord, placental tissue) may be collected for research. Samples that are normally collected by any invasive medical procedure other than blood sampling (e.g., cervical sampling, amniotic fluid) will only be collected at the time of an otherwise clinically indicated collection procedure.

Maternal blood samples will be obtained at enrollment and at specified times during pregnancy, during the hospital admission for childbirth, and until the 6+ weeks PP (non-pregnant baseline) last sample is drawn. If the hemophilia A genotype-positive mother receives treatment for hemophilia, samples will be timed with treatment monitoring whenever possible. At the time of delivery, cord blood and placental tissues will be sampled.

For the pediatric participants, an extra research sample will be collected during standard newborn screening, and a neonatal research blood draw will be requested in the first days of life if one is not ordered for clinical purposes. The study blood sampling schema is designed to ensure a minimum of two pre-FVIII exposure blood samples for all infants regardless of timing of the first FVIII ED. Thereafter, pediatric blood sampling will follow a time- and event-based sampling protocol for the duration of the study. Briefly, one to two research blood samples will be collected around specified EDs. If no research blood sample has been collected for 3 months, a research blood draw will be requested. This time-based schema allows sampling to coincide at least twice annually with other early life immunologic events. Two additional blood samples to enable cellular immunology studies will be collected between ED 20 and 50 or between ages 18 and 24 months, whichever comes first. If the child is reported by the laboratory to have a positive first-time clinical FVIII inhibitor test result, a sample will be requested to be drawn within 2-6 weeks of the inhibitor-positive blood draw for confirmatory testing. HARP will follow NIH guidance to cap the total pediatric blood volumes drawn to the weight- and time-based maximum volumes recommended (see Appendix 12.2 of the protocol). HARP will additionally follow European Union guidance to cap daily blood volumes drawn for research in the neonatal period (see Appendix 12.2 of the protocol).

Maternal participants will have a clinical genotype sent to the HARP Central Laboratory at the beginning of the study if a clinical genotype is not already established. All pediatric participants will have clinical hemophilia A genotyping and FVIII inhibitor testing performed via the HARP Central Laboratory. All other clinical tests will be performed locally.

Data will be collected longitudinally throughout the study, including medical records, electronic health record data, photographs and imaging data, and patient-reported outcomes (PROs) using questionnaires and diaries. Race, ethnicity, and social determinants of health are implicated in both maternal hemorrhage and childhood immune status, and these data will be gathered. Questionnaires will be administered to the hemophilia A genotype-positive mother to capture bleeding, other medical conditions and events, and PRO and well-being measures including measures of QOL. Tools will be adapted from existing questionnaires (e.g., PROMIS-29, ISTH-BAT, interim bleeding score, self-BAT, PBAC, PHQ-8, PhenX Toolkit, infant feeding). Hemophilia A genotype-positive mothers will be provided with a study diary to track bleeding, medical events, treatments, efficacy, and other basic medical information (e.g., other medications, other new diagnoses) for themselves and their child, including immunologic events such as illnesses, infections, and immunizations for the child.

Blood relative participants will answer questionnaires, release medical records, and have biological samples collected. The primary sample type is expected to be blood, other samples such as cheek swabs may also be collected.

The study will perform data analyses, immunologic, coagulation, genomics and other -omics research investigating the study hypotheses. Data and samples collected throughout the study will be saved in a shareable resource to support future research.

Maternal Inclusion Criteria:

Pregnant individuals who meet the following criteria are eligible for enrollment as study participants:

• Currently pregnant and prior to 37 weeks gestation
• Known to have or at-risk of having a severe hemophilia A genotype
• Pregnant with at least one fetus at-risk of inheriting severe hemophilia A
• Ability to understand and willingness to provide informed consent
• 18 years of age or older

Before the 38th week of pregnancy, enrolled participants must meet all the following criteria to continue to remain in the study:

• The pregnant mother has a severe hemophilia A genotype.
• A fetus is determined to have a >/= 25% risk of inheriting severe hemophilia A, or prenatal testing indicates a fetus is affected by severe hemophilia A.
• No other discontinuation criteria have been identified.

Pediatric Continuation / Inclusion Criteria:

Eligibility of the child to continue is assessed by age 8 weeks. Mother-child pairs in which a child meets the following criteria will remain in the study:

• Severe hemophilia A defined by a baseline FVIII:C < 0.01 IU/mL (or FVIII:C < 1%) or a genotype predicted to cause severe hemophilia A
• Born to a mother participating in the study

Thereafter, mothers and their children will continue in the study as long as no new discontinuation criteria occur.

Inclusion Criteria for Blood Relatives:

Blood relatives of the child may be offered participation if one of the following criteria are met:

• First-degree blood relatives (e.g., father, sibling) of the child
• Second-degree blood relatives (e.g., aunt, uncle, grandparent, half-sibling) of the child
• Any more distant male or female blood relative whose data or samples may be informative for the planned genetic studies of hemophilia and inhibitors

Exclusion/Discontinuation Criteria:

Maternal: For the pregnant person, exclusion or discontinuation criteria are as follows:

• Genetic testing is negative for a severe hemophilia A genotype
• Prenatal clinical diagnostic testing that indicates there is no fetus affected with severe hemophilia A
• Presence of another clinically significant bleeding disorder
• Participation in another study for which any blood collection total would exceed safety limits defined in this study
• Will deliver outside the United States or plans for regular pediatric care for the child to be delivered outside the United States
• Is a prisoner
• Any other reason that, in the opinion of the investigator, would render the individual unsuitable for participation in the study
• Inability for study team to obtain translated study documents in time for participation if participant is not fluent in English

Pediatric: For the child, discontinuation criteria are as follows:

• Infant does not have severe hemophilia A defined by a baseline FVIII:C < 0.01 IU/mL (or FVIII:C < 1%) or does not have a genotype predicted to cause severe hemophilia A
• Mother or child did not have minimal required study samples or data collected before birth, around the time of delivery, or in the neonatal period
• Child has another clinically significant bleeding disorder
• Child has a clinically severe immune disorder
• Participation in another study for which any blood collection total would exceed safety limits defined in this study
• Any other reason that, in the opinion of the investigator, would render the individual unsuitable for participation in the study

To accomplish the goal of following 50 mother-child pairs with a child affected by severe hemophilia A from pregnancy through at least the first 2 years of life, we expect to enroll approximately 120 pregnant mothers with a pregnancy at-risk of being affected by severe hemophilia A. Blood relatives of the child can also enroll.

The study will follow the NIH policies on data sharing and genomic data sharing. At completion, de-identified study data will be deposited into shareable databases such as BioData Catalyst and/or BIoLINcc and genomic data will be submitted to dbGAP and other data repositories as appropriate.

Study protocol and informed consents will be available on request starting Nov 2024 and will be on study website in 2026. The Clinical data will be available to qualified researchers with approved applications upon completion of primary analysis in late 2029. Results will be presented in meetings, published in journals, and shared widely with the community.

Qualified researchers will apply for approval from the HARP Research Access Committee, expected to form in late 2029.