This clinical trial is for adults who have congenital antithrombin deficiency (which is a disorder of blood clotting) and who are scheduled to undergo surgery OR childbirth in the near future.
   
The purpose of this study is to show how well the study drug Atenativ works at preventing clotting events during surgical procedures and childbirth in patients with congenital antithrombin deficiency. The study will also investigate the safety of Atenativ. Atenativ has already been approved in about 30 countries worldwide. However, Atenativ is not yet approved by the U.S. Food and Drug Administration (FDA) for use in the USA and is therefore considered an experimental drug in the United States.
   
This study will enroll two different types of participants:
   --Patients who are not pregnant and who are undergoing an elective surgery associated with a
   high risk of abnormal blood clotting events.
   --Patients who are pregnant and who are scheduled for caesarean section or delivery.
   
For participants who are due to undergo surgery, one infusion of Atenativ will be administered to them before the surgery and then as needed afterwards. These participants will stay at the hospital for at least 2 days after the surgery and will return to the study site for a follow-up visit at around 7 days afterwards. 

For participants who are due to undergo caesarean sections and deliveries, one infusion of Atenativ will be administered to them before the caesarean section or delivery and then as needed afterwards. These participants will stay at the hospital for at least 2 days after the caesarean section or delivery and will return to the study site for a follow-up visit at around 7 days afterwards. 

During the study, all participants will be asked to undergo a series of examinations, including having their blood drawn at multiple timepoints. Participants will be in the study for about 75 days, which includes screening, hospital stay, and two telephone assessments 14 (±2) and 30 (±2) days after study drug regimen initiation.