Decreased inferior vena cava diameter as an early marker in postpartum hemorrhage.

OBJECTIVES: To examine the association between inferior vena cava (IVC) diameter and postpartum blood loss and assess whether IVC diameter is a useful marker in the evaluation of intravascular volume status in women with postpartum hemorrhage (PPH). METHODS: This was a prospective case-control study conducted in a university medical teaching center in Afula, Israel, between November 2018 and March 2020. The study cohort consisted of women with a singleton pregnancy who delivered vaginally at term. The PPH group included women diagnosed with PPH based on visually estimated blood loss of 1000 mL or more at the time of enrolment. Hemodynamically unstable women or women with major bleeding at the time of diagnosis were not included. The control group consisted of women with an uneventful fourth stage of labor. IVC diameter was measured using transabdominal ultrasonography during inspiration (IVCi diameter) and expiration (IVCe diameter), and the collapsibility index was calculated ((IVCe - IVCi)/IVCe × 100). The primary outcome was the percentage difference in IVC diameter and collapsibility index between the PPH group and controls. The performance of the IVC collapsibility index in the prediction of the need for blood transfusion in women with PPH was assessed. In order to demonstrate a difference of 20% with a power of 80% and alpha of 0.05, 108 women, at a ratio of 1:2 in the study and control groups, respectively, were needed. RESULTS: Overall, 36 and 72 women were included in the final analysis in the PPH and control groups, respectively. IVCi and IVCe diameters were significantly smaller in the PPH group (0.93 ± 0.30 cm and 1.26 ± 0.32 cm, respectively) than in controls (1.42 ± 0.31 cm and 1.75 ± 0.28 cm, respectively) (P = 0.001 for both). The percentage reductions in IVCi and IVCe diameters in the PPH group compared with controls were 35.0% and 28.0%, respectively. IVC collapsibility index was increased significantly, by 42.9% (26.04 ± 8.67% vs 18.15 ± 5.07%; P = 0.001) in the PPH group compared with controls. IVC collapsibility index was a significant predictor of the need for blood transfusion and correctly predicted 81% of cases. Logistic regression analysis demonstrated that IVC collapsibility index was also a significant predictor of a drop in hemoglobin level of ≥ 2 g/dL (P = 0.001). CONCLUSIONS: IVC diameter changes in response to postpartum blood loss. Measurement of IVC diameter using transabdominal ultrasonography is an objective and useful non-invasive method for the early evaluation of intravascular volume status in women with PPH and for the prediction of cases that might require blood transfusion. © 2021 International Society of Ultrasound in Obstetrics and Gynecology.