An AE is defined as any untoward medical occurrence in a subject or clinical investigation subject administered a pharmaceutical product and which does not necessarily have a causal relationship with this treatment.

All 595 subjects in the Safety Population are included in the analysis of this outcome measure. Safety Population includes all enrolled subjects who received at least one injection of study treatment in feeder study C87031 [NCT00152490] or C87032 [NCT00152425].

An SAE is defined as any untoward medical occurrence that occurs at any dose which results in death, is life threatening, requires hospitalization, results in persistent/significant disability/incapacity, is an infection that requires parenteral antibiotics, is a congenital anomaly/birth defect, or is an important medical event.

All 595 subjects in the Safety Population are included in the analysis of this outcome measure. Safety Population includes all enrolled subjects who received at least one injection of study treatment in feeder study C87031 [NCT00152490] or C87032 [NCT00152425].

HBI remission is defined as total HBI score of 4 points or less. HBI score consists of clinical parameters of general well-being (0 to 4), abdominal pain (0 to 3), number of liquid stools per day, abdominal mass (0 to 3), and complications (8 items, score 1 per item) lower scores indicating better well being. The first three parameters are scored for the previous day.

Of the 594 subjects in the Intention-To-Treat (ITT) Population, 592 subjects are included in the analysis of this outcome measure. ITT Population includes all subjects of the Safety Population who provide at least one efficacy measurement after Week 0 of this study.

Response is defined as decrease in total Harvey Bradshaw Index (HBI) score of 3 or more points. HBI score consists of clinical parameters of general well-being (0 to 4), abdominal pain (0 to 3), number of liquid stools per day, abdominal mass (0 to 3), and complications (8 items, score 1 per item) lower scores indicating better well-being. The first three parameters are scored for the previous day.

All 594 subjects in the Intention-To-Treat (ITT) Population are included in the analysis of this outcome measure. ITT Population includes all subjects of the Safety Population who provide at least one efficacy measurement after Week 0 of this study.

Plasma samples for determination of Certolizumab Pegol were taken prior to Certolizumab Pegol administration.

Of the 595 subjects in the Safety Population, 590 subjects are included in the analysis of this outcome measure. Safety Population includes all enrolled subjects who received at least one injection of study treatment in feeder study C87031 [NCT00152490] or C87032 [NCT00152425].

Subjects are counted as antibody positive to Certolizumab Pegol if they have at least one positive result from Week 0 in one of the previous studies CDP870-031 [NCT00152490] or CDP870-032 [NCT00152425] to the Last Visit in this study. A positive result is defined as Anti-CZP antibody levels > 2.4 units/mL.

Of the 595 subjects in the Safety Population, 593 subjects are included in the analysis of this outcome measure. Safety Population includes all enrolled subjects who received at least one injection of study treatment in feeder study C87031 [NCT00152490] or C87032 [NCT00152425].

Of the 594 subjects in the Intention-To-Treat (ITT) Population, 593 subjects are included in the analysis of this outcome measure. ITT Population includes all subjects of the Safety Population who provide at least one efficacy measurement after Week 0 of this study.

Of the 594 subjects in the Intention-To-Treat (ITT) Population, 567 subjects are included in the analysis of this outcome measure. ITT Population includes all subjects of the Safety Population who provide at least one efficacy measurement after Week 0 of this study.