Pregnancy complications, such as placenta previa, are problems that occur only during pregnancy. They may affect the woman, the fetus, or both and may occur at different times during the pregnancy. However, most pregnancy complications can be effectively treated.
Normally, the placenta is located in the upper part of the uterus. In placenta previa, the placenta is located in the lower part. It covers the opening of the cervix—the entrance to the birth canal. Sometimes the placenta is located near the opening of the cervix, not over it (called a low-lying placenta).
Placenta previa occurs in about 1 of 250 deliveries. During the 2nd trimester, as many as 2% of pregnant women have placenta previa. Placenta previa may be visible on ultrasonography. However, it resolves on its own in more than 90% of women before they deliver. If it does not resolve, the placenta may detach from the uterus, depriving the baby of its blood supply. Passage of the baby through the birth canal can also tear the placenta, causing severe bleeding.
Risk factors (conditions that increase the risk of a disorder) for placenta previa include the following:
Having had more than one pregnancy
Having had a cesarean delivery
Having a structural abnormality of the uterus, such as fibroids Fibroids A fibroid is a noncancerous tumor composed of muscle and fibrous tissue. It is located in the uterus. Fibroids can cause pain, abnormal vaginal bleeding, constipation, repeated miscarriages... read more
Having had a procedure that involves the uterus such as removal of fibroids from the uterus (myomectomy Surgery for fibroids A fibroid is a noncancerous tumor composed of muscle and fibrous tissue. It is located in the uterus. Fibroids can cause pain, abnormal vaginal bleeding, constipation, repeated miscarriages... read more ) or dilation and curettage Dilation and Curettage Sometimes doctors recommend screening tests, which are tests that are done to look for disorders in people who have no symptoms. If women have symptoms related to the reproductive system (gynecologic... read more (D and C) done several times
Placenta previa can cause painless bleeding from the vagina that suddenly begins late in pregnancy. The blood may be bright red. Bleeding may become profuse, endangering the life of the woman and the fetus.
Placenta previa can cause problems for the fetus, such as the following:
The fetus may not grow as much as expected (intrauterine growth restriction Small-for-Gestational-Age (SGA) Newborn A newborn who weighs less than 90% of newborns of the same gestational age at birth (below the 10th percentile) is considered small for gestational age. Newborns may be small because their parents... read more ).
The membranes around the fetus may rupture too soon (premature rupture of the membranes Prelabor Rupture of the Membranes (PROM) Prelabor rupture of the membranes is the leaking of amniotic fluid from around the fetus at any time before labor starts. After the membranes rupture, labor often soon follows. If labor does... read more ).
Blood vessels connecting the umbilical cord and placenta may block the fetus's exit through the opening of the cervix (vasa previa Vasa Previa In vasa previa, membranes that contain blood vessels connecting the umbilical cord and placenta lie across or near the opening of the cervix—the entrance to the birth canal. Vasa previa may... read more ).
If women have had a cesarean delivery, placenta previa increases the risk that the placenta will be too firmly attached to the uterus (placenta accreta Placenta Accreta Placenta accreta is a placenta with an abnormally firm attachment to the uterus. Having had both a cesarean delivery and placenta previa in a previous pregnancy greatly increases the risk of... read more ). Placenta accreta belongs to a group of disorders called the placenta accreta spectrum. These disorders differ in how firmly the placenta is attached to the uterus.
Doctors suspect placenta previa in pregnant women with vaginal bleeding that starts after 20 weeks of pregnancy. Ultrasonography helps doctors identify placenta previa and distinguish it from a placenta that has detached too early (placental abruption Placental Abruption Placental abruption is the premature detachment of a normally positioned placenta from the wall of the uterus, usually after 20 weeks of pregnancy. Women may have vaginal bleeding and/or severe... read more ).
If placenta previa is causing symptoms, doctors monitor the fetus's heart rate Fetal monitoring Labor is a series of rhythmic, progressive contractions of the uterus that gradually move the fetus through the lower part of the uterus (cervix) and birth canal (vagina) to the outside world... read more to determine whether the fetus is having problems, such as not getting enough oxygen.
Problems With the Placenta
When bleeding is minor and occurs before about 36 weeks of pregnancy, doctors typically advise that the woman be admitted to the hospital and told to limit her activity until the bleeding stops. Limiting her activity (called modified activity or modified bed rest) means that she should stay off her feet for most of the day. If the bleeding stops, the woman may be allowed to gradually resume light activities. If bleeding does not recur, she is usually sent home, provided that she can return to the hospital easily. Doctors advise against sexual intercourse, which can trigger bleeding.
If bleeding recurs, the woman is usually readmitted to the hospital and may be kept there until delivery.
Some experts recommend using corticosteroids to help the fetus's lungs mature when early delivery—usually before about 34 weeks of pregnancy—may become necessary.
If the woman is not having contractions and if bleeding has stopped, doctors may deliver the baby at 36 to 37 weeks of pregnancy.
Delivery is usually done immediately when one of the following occur:
In women with placenta previa, delivery is cesarean Cesarean Delivery Cesarean delivery is surgical delivery of a baby by incision through a woman’s abdomen and uterus. In the United States, up to 30% of deliveries are cesarean. Doctors use a cesarean delivery... read more , done before labor starts.
Women who bleed profusely may need blood transfusions.