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
