A placenta previa (thanks to midwifemuse.wordpress.com for this image) is found when the placenta gets implanted right over the internal opening of the cervical canal. This can cover the opening totally (completel placenta previa), partially (partial placenta previa) or marginally (marginal placenta previa). In about 1 in 200 live births placenta previa occurs and in about 20% of these it is the more dangerous form, the total placenta previa.
The main symptoms are painless bleeding in the last part of the pregnancy. However, the diagnosis is usually made much earlier, at about 17 weeks when the initial ultrasound is ordered. At that time about 10% of pregnant women will show some form of placenta previa.
However, there is a phenomenon of “placental migration”, which clears the inner opening of the cervical canal in more than 90% of these cases. This is why only 1 in 200 patients will need a cesarian section at the end (Ref. 18, p. 511). However, about 25% of the initially (at 17 weeks) diagnosed total placenta previa cases will persist at the time of he delivery. It is absolutely necessary for the pregnant woman to know that she has this condition, as the delivery should be done by cesarean section.
Occasionally an obstetrician opts for a “double set-up” for a marginal placenta previa, where a trial conventional labor is started under highly monitored conditions, but with the anesthetist and neonatologist standing by and the set-up for an emergency cesarean section in the same room.
Placenta previa – Important fact to remember
If it is known from an ultrasound exam that there is a placenta previa, never allow a health care provider to examine vaginally. Otherwise serious bleeding can occur from this resulting in shock and death of the mother!
This way, if sudden bleeding should be encountered a caesarean delivery can very quickly be done. However, most physicians likely will do an elective caesarian section near the estimated date of confinement.
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