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Estimates intraoperative blood loss in obstetrics by two methods: gravimetric (weighed sponges/drapes, 1 g ≈ 1 mL blood) and hematocrit-based (EBL = estimated blood volume × (pre-Hct − post-Hct)/pre-Hct, using a pregnancy blood volume of approximately 85 mL/kg). Postpartum hemorrhage is defined as cumulative blood loss ≥ 1000 mL within 24 hours.
Clinical decision-support tool for qualified healthcare professionals. Results are not a diagnosis and should not replace professional clinical judgment.
Estimated blood loss in obstetrics is typically quantified by the gravimetric method (weighing blood-soaked materials; 1 g ≈ 1 mL) and/or calculated from hematocrit: EBL = blood volume × (pre-Hct − post-Hct)/pre-Hct. Blood volume in pregnancy averages ~85 mL/kg (range 70–100 mL/kg). ACOG (Obstetric Hemorrhage, CO 794) defines postpartum hemorrhage as cumulative blood loss ≥ 1000 mL or bleeding with signs of hypovolemia within 24 hours of delivery.
Specialty
ObstetricsCategory
Obstetrics & GynecologyDifficulty
Basic
Estimated Time
30 seconds
Version
1.0
Last Updated
2026-08-16
Formula
Keywords
Normal Range
ACOG defines postpartum hemorrhage as cumulative blood loss ≥ 1000 mL (or bleeding with signs of hypovolemia) within 24 hours of delivery, regardless of route of delivery.
| Classification | Range |
|---|---|
Expected vaginal delivery (typical) | < 500 mL |
Increased / concern monitor closely | 500–999 mL |
Postpartum hemorrhage ACOG definition; respond urgently | ≥ 1000 mL |
Estimates obstetric blood loss by the gravimetric method (weighed sponges and drapes; 1 g ≈ 1 mL) or the hematocrit-based method (EBL = estimated blood volume × (pre-Hct − post-Hct)/pre-Hct, with a pregnancy blood volume of ~85 mL/kg).
Blood loss is estimated by one of two methods. Gravimetric: EBL (mL) = (wet weight - dry weight) in grams x 1 mL/g. Hematocrit-based: EBL = estimated blood volume x (pre-Hct - post-Hct) / pre-Hct, where blood volume is approximately 85 mL/kg.
Selects the gravimetric (weighed materials) or hematocrit-based method; only the corresponding inputs are used.
Weight of blood-soaked sponges and drapes in grams, used in the gravimetric method.
Baseline weight of dry materials in grams, subtracted from wet weight in the gravimetric method.
Maternal weight in kg, multiplied by approximately 85 mL/kg to estimate blood volume in the hematocrit method.
Pre-delivery hematocrit in percent, the denominator of the hematocrit method.
Post-delivery hematocrit in percent, subtracted from the pre-delivery hematocrit.
Cumulative blood loss ≥ 1000 mL within 24 hours (or bleeding with signs of hypovolemia) meets the ACOG definition of postpartum hemorrhage. Loss of 500–999 mL exceeds typical expectations and warrants close monitoring; < 500 mL is within the expected range for delivery.
Quantitative assessment of blood loss is a cornerstone of postpartum hemorrhage recognition and response; early identification of ≥ 1000 mL loss triggers protocol-based management that reduces maternal morbidity and mortality.
A 70 kg patient has a pre-delivery hematocrit of 36% and a post-delivery hematocrit of 30%.
Inputs:
Expected Result: Estimated blood loss ~992 mL (BV 5,950 mL × 6/36) — above the typical expected loss; monitor closely with the hemorrhage protocol ready.
Maternal blood volume expands during pregnancy to approximately 85 mL/kg (range 70–100 mL/kg). Using the non-pregnant ~70 mL/kg underestimates total blood volume and can overestimate proportional loss.
ACOG defines PPH as cumulative blood loss ≥ 1000 mL, or bleeding with signs/symptoms of hypovolemia, within 24 hours after delivery — regardless of delivery route.
Disclaimer: This calculator is intended for educational and clinical decision support purposes only. Blood-loss estimates are imprecise; clinical signs of hypovolemia always take precedence in hemorrhage management.