Factor XI (plasma)
Factor XI is part of the intrinsic (contact activation) coagulation pathway. Unlike many clotting factors that increase substantially in pregnancy, Factor XI levels change only modestly and may decrease slightly in late gestation.
| Units | Nonpregnant Adult | 1st Trimester | 2nd Trimester | 3rd Trimester |
|---|---|---|---|---|
| % | 50 – 150 | 80 – 127 | 82 – 144 | 65 – 123 |
Pregnancy physiology
- Factor XI does not show the marked gestational rise seen with Factors VII, VIII, and fibrinogen.
- Mild decreases in late pregnancy may be physiologic.
- Levels >30–40% are often adequate for routine hemostasis in most patients.
Causes of low Factor XI
- Inherited Factor XI deficiency (hemophilia C)
- Severe liver disease
- Disseminated intravascular coagulation (DIC)
- Massive transfusion (dilutional)
Bleeding risk correlates poorly with absolute level and is best predicted by personal bleeding history.
Causes of elevated Factor XI
- Acute inflammatory states
- Estrogen exposure
- Association with venous thrombosis risk in nonpregnant populations
Clinical interpretation & pregnancy considerations
- Levels <15–20% are associated with increased operative and postpartum hemorrhage risk.
- Values 20–40% confer variable bleeding risk depending on prior surgical history.
- Third-trimester assessment is recommended in known deficiency.
- Delivery and neuraxial anesthesia planning should involve hematology for low levels.
- Postpartum re-testing (6–12 weeks) helps distinguish transient pregnancy effects from true deficiency.
References
- Abbassi-Ghanavati M, Greer LG, Cunningham FG. Pregnancy and laboratory studies: a reference table for clinicians. Obstet Gynecol. 2009;114:1326–31.