Protrusion of a part of the placenta over the exit (cervical canal) from the uterine cavity may result in premature onset of labour and post-traumatic or spontaneous bleeding before and during labour. Incidence of placenta previa decreases progressively during pregnancy, as the placenta tends to "migrate" away from the cervical canal.
Placement of the diagnostic ultrasound probe in the vagina (transvaginal) is more accurate than traditional abdominal ultrasound for diagnosing presence and severity of placenta previa, .
If it is identified on routine pregnancy ultrasound, the disappearance or persistence of previa must be monitored  as the pregnancy proceeds.
management of placenta previa includes:
Failure to confirm migration of the placenta away from the cervix occasionally results in potentially preventable catastrophic hemorrhage and may therefore be actionable.
Nevertheless, there is recent agreement ,  that mothers-to-be need not necessarily remain hospitalised even after significant bleeding. The outcome is comparable, with  or without  bedrest at home. Exercise and sexual intercourse need generally be restricted only after they have provoked bleeding.
Recurrence of hemorrhage or premature labour after hospital discharge does not necessarily indicate substandard care
If the previa is marginal, attempt at vaginal delivery is a matter of clinical judgment, but initial vaginal examination for induction of labour requires immediate access to cesarian section  ("double set-up") in case of a catastrophic hemorrhage.
Substandard care of placenta previa can result in stillbirth, newborn death and threat to the mother's life
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