Placenta Previa Classifications And Evaluation

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Placenta Previa

Placenta Previa

Placenta Previa: Is the development of the placenta in the lower uterine segment, partially or completely covering the internal cervical os.


Traditionally categorized into 3 types:

1- Complete, total or central Previa: internal os entirely covered.

2- Partial : internal os partially covered.

3- Marginal : placenta reaches the edge of the internal os.


– Specific causes are unknown.

Implantation may be affected by:
1. Abnormality of endometrial vascularity.

2. Delayed ovulation.

3. Prior endometrial trauma.

4. Multiple pregnancies.

5. Previous uterine surgery.

Clinical manifestations:

– Usually presents as painless vaginal bleeding in the 3rd trimester but can occur as early as 20 weeks of gestation bleeding occurs without warning in the absence of trauma.

– Blood loss from the first bleeding is rarely fatal, in each subsequent episode bleeding is heavier.

– Placenta previa may not cause bleeding until labor begins, or complete dilatation has occurred.

– Bleeding occurs earlier and is more profuse with total placenta previa.

Diagnostic evaluation:

– Painless vaginal bleeding is placenta previa until proven otherwise.

– Ultrasound is the diagnostic technique of choice.

– Definitive diagnostic by direct palpation of the placenta is not recommended.

Vaginal examination ” double setup procedure “:
– Under sterile technique by the physician after diagnosis by ultrasound.

– Inconclusive ultrasound or only low –lying placenta noted.

Note: the term low-lying implantation is used when the placenta situated in the lower uterine segment but away from the os.

– Sterile speculum examination performed first.

– It is attempted only if the physician and the women are prepared for cesarean delivery in the operating room.

– If greater than 3cm dilated and no placenta covering os, then perform amniotomy ( by the physician).

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