Factor IX (plasma)
Factor IX (Christmas factor) is a vitamin K–dependent coagulation factor in the intrinsic pathway. During pregnancy, activity increases as part of the physiologic hypercoagulable state.
| Units | Nonpregnant Adult | 1st Trimester | 2nd Trimester | 3rd Trimester |
|---|---|---|---|---|
| % | 50 – 150 | 103 – 172 | 154 – 217 | 164 – 235 |
Pregnancy physiology
- Factor IX activity normally increases across gestation.
- Levels rise most prominently during the second and third trimesters.
- This contributes to the overall hypercoagulable state of pregnancy.
Causes of elevated Factor IX
- Normal pregnancy physiology
- Acute inflammation or infection
- Estrogen exposure
- Independent venous thromboembolism risk factor when persistently elevated
Markedly elevated Factor IX (>150–200%) has been associated with increased thrombotic risk outside pregnancy.
Causes of low Factor IX
- Hemophilia B (Factor IX deficiency)
- Severe liver disease
- Vitamin K deficiency
- Warfarin or vitamin K antagonists
- Disseminated intravascular coagulation (DIC)
Clinical interpretation & pregnancy considerations
- Carriers of hemophilia B may have reduced activity and increased bleeding risk.
- Severe deficiency is defined as <1%, moderate 1–5%, mild 5–40%.
- Peripartum management requires coordination with hematology and anesthesia.
- Neuraxial anesthesia is typically targeted at Factor IX ≥ 50%.
- Always interpret with PT/INR, aPTT, platelet count, liver function, and bleeding history.
References
- Abbassi-Ghanavati M, Greer LG, Cunningham FG. Pregnancy and laboratory studies: a reference table for clinicians. Obstet Gynecol. 2009;114:1326–31.