Normal Fibrinogen Level in the Second Trimester of Pregnancy
Fibrinogen levels in the second trimester of pregnancy typically range from 3.4 to 8.5 g/L, representing a physiologic increase above non-pregnant values as part of the hypercoagulable state of pregnancy. 1
Trimester-Specific Reference Ranges
Second Trimester Values
- Primary reference range: 3.4–8.5 g/L based on research establishing pregnancy-specific intervals 1
- Alternative reported range: 2.6–6.6 g/L from earlier studies, though this may underestimate the upper limit 1
- Fibrinogen begins rising significantly from the first trimester and continues to increase progressively throughout pregnancy 2, 3
Comparative Context Across Pregnancy
- First trimester: 2.6–6.6 g/L 1
- Second trimester: 3.4–8.5 g/L 1
- Third trimester: 3.7–6.2 g/L (with median 3.86 g/L at 36 weeks) 2
- The progressive rise reflects increasing coagulation factor production as pregnancy advances toward term 2
Clinical Interpretation Framework
Normal Physiologic Elevation
- Fibrinogen functions as an acute phase reactant and increases throughout pregnancy as part of the normal hypercoagulable adaptation 2
- Mean fibrinogen levels exceed conventional non-pregnant reference intervals as early as 16 weeks gestation 4
- This elevation represents a protective mechanism against postpartum hemorrhage rather than pathology 2
Pathologic Thresholds to Recognize
- Fibrinogen <3 g/L carries significant clinical weight in pregnancy-specific DIC scoring systems 2
- Fibrinogen ≤2 g/L has 100% positive predictive value for severe postpartum hemorrhage 2
- Fibrinogen <1.5 g/L in the second trimester warrants fibrinogen replacement in women with congenital hypofibrinogenemia to prevent placental abruption 2
Risk Factor Adjustments
Gestational Diabetes Impact
- Women with gestational diabetes mellitus (GDM) demonstrate significantly higher fibrinogen concentrations compared to those without GDM (p=0.0449) 1
- Adjusted reference ranges accounting for GDM: 3.4–8.84 g/L in the second trimester 1
Smoking Considerations
- Nicotinism compounds the physiologic increase in fibrinogen during pregnancy 1
- Reference values require upward adjustment when these risk factors are present 1
Common Clinical Pitfalls
Misapplication of Non-Pregnant Ranges
- Standard laboratory reference intervals (typically 1.8–3.5 g/L or 2.0–4.0 g/L for non-pregnant adults) are inappropriate during pregnancy 4
- Using non-pregnant cutoffs will incorrectly flag most healthy pregnant women as abnormal by the second trimester 4
Misinterpretation of Elevated Values
- Elevated fibrinogen in pregnancy indicates normal physiologic adaptation and increased thrombotic risk, not bleeding risk 2
- Only critically low fibrinogen (<1.5–2.0 g/L) predicts hemorrhagic complications 2