Evidence‑Based Fibrinogen Thresholds in Pregnancy

Reference Values from Clinical Studies

The median fibrinogen concentration at 36 weeks gestation is approximately 386 mg/dL (3.86 g/L) in uncomplicated pregnancies, based on a 2020 cohort analysis (Journal of Thrombosis and Haemostasis) 1.

A fibrinogen level < 300 mg/dL (< 3 g/L) is incorporated as a key criterion in pregnancy‑specific disseminated intravascular coagulation (DIC) scoring systems (Journal of Thrombosis and Haemostasis, 2020) 1.
A fibrinogen level ≤ 200 mg/dL (≤ 2 g/L) yields a 100 % positive predictive value for severe postpartum hemorrhage, indicating a strong diagnostic threshold (Journal of Thrombosis and Haemostasis, 2020) 1.

In the second trimester, a fibrinogen concentration < 150 mg/dL (< 1.5 g/L) prompts fibrinogen replacement therapy in women with congenital hypofibrinogenemia to prevent placental abruption (Journal of Thrombosis and Haemostasis, 2024) 2.
Women with congenital fibrinogen disorders should aim to keep trough fibrinogen levels ≥ 100 mg/dL (≥ 1 g/L) throughout pregnancy; if this target is unattainable, maintaining 50–100 mg/dL (0.5–1 g/L) during the first two trimesters is acceptable (Journal of Thrombosis and Haemostasis, 2024) 2.
For cases of vaginal bleeding or placental abruption, the recommended target fibrinogen level is ≥ 150 mg/dL (≥ 1.5 g/L) to mitigate hemorrhagic risk (Journal of Thrombosis and Haemostasis, 2024) 2.

In pregnant women, fibrinogen rises progressively from the first trimester and continues to increase throughout gestation, reflecting heightened coagulation factor production as term approaches. 3
The second‑trimester reference interval is 3.4 – 8.5 g/L. 3
In the third trimester, fibrinogen values range from 3.7 – 6.2 g/L, with a median of approximately 3.86 g/L at 36 weeks gestation. [3][4]

Fibrinogen acts as an acute‑phase reactant and its elevation during pregnancy is a normal hypercoagulable adaptation that protects against postpartum hemorrhage rather than indicating pathology. 3

A fibrinogen concentration < 3 g/L is a key criterion in pregnancy‑specific disseminated intravascular coagulation (DIC) scoring systems. 3
A fibrinogen level ≤ 2 g/L yields a 100 % positive predictive value for severe postpartum hemorrhage. 3
In the second trimester, fibrinogen < 1.5 g/L warrants fibrinogen replacement therapy in women with congenital hypofibrinogenemia to prevent placental abruption. 5

Elevated fibrinogen in pregnancy denotes a normal physiologic response and an increased thrombotic risk; it does not signify a bleeding risk. 3
Only critically low fibrinogen levels (approximately < 1.5 – 2.0 g/L) are predictive of hemorrhagic complications. [3][5]