Placenta Previa occurs when the placenta remains low in the uterus and may partially or sometimes completely cover the cervix. While common in early pregnancy before 20 weeks, it usually affects only 1 of 200 women by the third trimester.
There are three grades of previa: marginal occurs when the placental edge is against the outer edge of the cervix, partial occurs when a part of the cervix is blocked by the placenta, and complete when the entire cervix is covered.
Although the symptoms are variable, it is usually suspected when pain-free bleeding occurs in the final trimester. Other conditions which may indicate some degree of previa include pre-term contractions, a transverse baby or one that is breech, or fundal measurements which are consistently larger than indicated by the baby's gestational age.
Treatment varies by the degree/severity. When diagnosed by ultrasound midway through a pregnancy, a late term repeat ultrasound around 28-32 weeks can be recommended to determine whether the placenta has moved up and away from the cervix, if no other symptoms like bleeding have been observed. Care providers may recommend that pregnant women with some degree of previa limit their travel, intercourse and pelvic exams to prevent the introduction of infection or increase the risk of bleeding. Previa and air travel usually don't mix.
If bleeding is occurring, bed rest may be required. If the bleeding is not well-controlled, steroid shots may be recommended to develop the baby's lungs in the event that the pregnancy is unable to continue to term. Maternal blood transfusions may be performed to combat blood loss. Hospitalization may be required for the remainder of the pregnancy.
Some marginal previa cases can still be delivered vaginally. Unfortunately, a persistent partial or complete previa will necessitate a cesarean section.
In cases of complete previa, cesarean section is almost always required before spontaneous labor begins to avoid a placental abruption. When this occurs, the placenta detaches from the uterine wall too early, which limits the baby's oxygen supply and may cause uncontrollable hemorrhaging in the mother. The oxygen deprivation to the baby from an abruption can lead to brain damage or other chronic conditions.
Hearing the news of previa can feel like your dream of a natural birth is being snatched away. It can be emotionally and physically draining. To help yourself through this time, there are support groups for mothers on bed rest or for those with placenta previa, including some online options. Don't be afraid to talk through your feelings with your birth companion, care provider, or a friend.
Routine early ultrasounds often detect this condition. However, since the placenta starts low and gradually moves up the uterine wall, the majority of these cases resolve spontaneously as the pregnancy advances. By refraining from routine ultrasound until 22-24 weeks, many mothers can be spared the worries of placenta previa which would have been present before this time.
Page Last Modified by Catherine Beier, MS, CBE
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