Placenta previa stages
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"placenta previa" AND classification
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placenta previa classification complete partial marginal low lying placenta current guideline
Placenta previa stages/types:
Traditional classification
-
Type I - Low-lying placenta
Placenta is in the lower uterine segment but does not reach the internal cervical os. -
Type II - Marginal placenta previa
Placental edge reaches the margin of the internal os but does not cover it. -
Type III - Partial placenta previa
Placenta partly covers the internal os. -
Type IV - Complete or central placenta previa
Placenta completely covers the internal os.
Current ultrasound-based terminology
The older four-type system is now used less often. Current practice generally describes:
- Low-lying placenta: placental edge is within 20 mm of the internal os, but does not cover it.
- Placenta previa (placenta praevia): placenta covers the internal os, whether partially or completely.
Transvaginal ultrasound is the most accurate way to determine the placental edge relative to the cervix. RCOG patient guidance uses this modern terminology.
New stages
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current placenta previa classification low lying placenta placenta previa internal os 20 mm guideline
The new classification does not use Stage/Type I-IV.
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Low-lying placenta
Placental edge is <20 mm from the internal cervical os, but does not cover it. -
Placenta previa (placenta praevia)
Placenta covers the internal cervical os, either partly or completely.
So, marginal, partial, and complete/central placenta previa are older terms and are no longer preferred in modern ultrasound reporting. The classification is based on transvaginal ultrasound, typically after 16 weeks. RCOG guidance
New stages pf placenta previa according to RCOg
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site:rcog.org.uk placenta praevia new classification stages low lying 20 mm RCOG 2026 guideline
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"placenta previa" AND classification
According to the RCOG classification, there are 2 categories, not four stages:
-
Low-lying placenta
The placental edge lies less than 20 mm from the internal cervical os, but does not cover it. -
Placenta praevia
The placenta lies directly over the internal cervical os, meaning it covers the cervix.
Therefore, the old terms Type I-IV, marginal, partial, and complete/central placenta previa are no longer used in RCOG reporting. This is based on ultrasound assessment, preferably transvaginal ultrasound when placental location needs clarification. RCOG definitions
New classification
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RCOG Green-top 27a definition low-lying placenta less than 20 mm placenta praevia directly over internal os classification
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"placenta previa" AND ultrasonography
RCOG ultrasound-based classification of placental location
| Category | Definition |
|---|---|
| Normal placenta | Placental edge is 20 mm or more from the internal cervical os |
| Low-lying placenta | Placental edge is less than 20 mm from the internal cervical os, but does not cover it |
| Placenta praevia | Placenta lies directly over / covers the internal cervical os |
- Apply this terminology after 16 weeks' gestation.
- Assessment is by ultrasound, with transvaginal ultrasound used to accurately define the relationship to the internal os.
- The old Type I-IV system, including marginal, partial, and complete/central placenta praevia, is not used in the current RCOG classification.
This is the definition used in the RCOG Green-top Guideline No. 27a.
Pph
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RCOG postpartum haemorrhage classification minor major moderate severe 500 1000 2000 mL guideline
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"postpartum hemorrhage" AND definition
RCOG classification of primary postpartum haemorrhage (PPH)
Primary PPH: Blood loss of 500 mL or more within 24 hours of birth.
| Category | Blood loss |
|---|---|
| Minor PPH | 500-1000 mL |
| Major PPH | >1000 mL |
| Moderate major PPH | 1000-2000 mL |
| Severe major PPH | >2000 mL |
Secondary PPH: Abnormal or heavy bleeding occurring from 24 hours to 12 weeks postpartum.
RCOG uses this volume-based classification in Green-top Guideline No. 52.
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