Fibrinogen (Plasma)
Fibrinogen is a critical coagulation factor and acute-phase reactant that rises substantially in normal pregnancy, providing protection against hemorrhage but also contributing to the hypercoagulable state.
| Units | Nonpregnant Adult | 1st Trimester | 2nd Trimester | 3rd Trimester |
|---|---|---|---|---|
| mg/dL | 233 – 496 | 244 – 510 | 291 – 538 | 373 – 619 |
| g/L | 2.3 – 5.0 | 2.4 – 5.1 | 2.9 – 5.4 | 3.7 – 6.2 |
Physiology in pregnancy
- Fibrinogen rises progressively beginning in early pregnancy.
- Third-trimester values often exceed 450–500 mg/dL.
- This rise provides protection against hemorrhage but increases thrombotic risk.
- Low‐normal fibrinogen in pregnancy is often clinically abnormal.
Causes of low fibrinogen
- DIC — placental abruption, IUFD, amniotic fluid embolism, HELLP, severe preeclampsia
- Massive obstetric hemorrhage
- Severe liver failure
- Congenital afibrinogenemia or hypofibrinogenemia
- Primary or secondary fibrinolysis
- Dilutional coagulopathy (large-volume resuscitation)
Causes of elevated fibrinogen
- Normal physiologic rise in pregnancy (late 2nd–3rd trimester)
- Acute inflammation or infection
- Chronic inflammatory disease
- Malignancy
- Tissue injury or trauma
- Nephrotic syndrome
- Smoking (mild elevation)
Clinical interpretation & obstetric considerations
- Fibrinogen <300 mg/dL in late pregnancy is highly concerning for evolving DIC.
- Levels <200 mg/dL are associated with severe obstetric hemorrhage.
- Early fibrinogen replacement is a cornerstone of massive transfusion protocols.
- Point-of-care TEG/ROTEM may underestimate early fibrinogen depletion if not fibrin-specific.
- Pregnancy reference ranges must be used—nonpregnant cutoffs are unsafe in obstetrics.
References
- Abbassi-Ghanavati M, Greer LG, Cunningham FG. Pregnancy and laboratory studies. Obstet Gynecol. 2009.
- Lockwood CJ. Hematology in pregnancy. 2011.
- British Committee for Standards in Haematology. DIC Guidelines. Br J Haematol. 2009.
- International Society on Thrombosis and Haemostasis (ISTH). DIC Guidance.
- ACOG Practice Bulletin No. 196. Thromboembolism in Pregnancy.
- SMFM Consult Series #47. Obstetric Hemorrhage.