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