Hemophilia A Research Program

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