Placenta Problems in Pregnancy

Two terms you may hear during your pregnancy are placental abruption and placenta previa. When the placenta detaches from the uterine wall, it is called placental abruption. When the placenta covers the mother’s cervix, it is called placenta previa. These are two very different conditions, but both involve problems with your baby’s placenta during pregnancy.

There are many possible causes for placental abruption. It’s often not possible to know exactly why a placenta begins to detach from the uterus. A common explanation is a uterine fibroid, which is a benign muscle tumor of the uterus, where the blood supply is usually the best. Placental abruption is remarkably increased by uterine surgery, and of course the most common uterine surgery is cesarean section. One prior C-section increases the abruption risk by roughly 40 to 74 percent and this increases with multiple C-sections. After two C-sections the risk is 30 percent higher than the risk with one C-section. The most likely explanation is interference of blood supply to the top of the uterus so that the placenta has a difficult time attaching. Another possible cause could be an infection in the lining of the uterus which causes difficulty for the placenta to attach to the uterine wall and to remain attached.

In the past when a woman had a placental abruption, we confined them to bedrest. Today, I would recommend decreasing activity. For example, for mothers who work outside the home, I recommend no work outside the home until after delivery. Decreasing any activity which puts pressure on the uterus is also recommended.

With placental abrution, there is the possibility of vaginal bleeding and the need for a C-section. For babies with placental abruption, preterm birth is the most common problem. In my experience, all moms and babies have survived placental abruption, although some of the babies were born preterm. Not very well understood or acknowledged is the fact that catastrophic abruption seldom occurs all at once. In my experience, the placenta tends to let go a piece at a time so there is enough warning to take action.

Placenta previa occurs when the placenta begins to cover the mother’s cervix. The placenta can impinge upon the cervix in many ways. The placenta previa can be near the cervix, covering a small portion of the cervix, covering the cervix halfway, or covering the cervix all way. Many women develop placenta previa at about 20 weeks. In my experience, it occurs at about 20 weeks in about 50 percent of pregnancies, or 1/2 of patients. There is almost no risk at this point in pregnancy, although most obstetricians would recommend pelvic rest which is a euphemistic term for no sexual intercourse. Placenta previas at 20 weeks are mostly benign because the placenta migrates from the lower part of the uterus to the upper part of the uterus as the uterus grows. The placenta travels along the uterus searching for the best supply of blood.

The best way to diagnose placenta previa is with an ultrasound. With a placenta previa, examination of the cervix with a finger is contraindicated because there is a significant risk of dislodging the placenta and causing bleeding.

If the placenta does not migrate upwards in the uterus but remains close to the cervix, there is the risk of continued bleeding and an eventual C-section. The good news is a placenta previa causing the death of the baby or mother is extremely rare, much less than 1 percent. Although delivery because of placenta previa is often preterm, the pregnancy usually survives until the baby is old enough to be delivered by C-section. The baby may be preterm, but is old enough to do well after delivery.

Placenta previa and placenta accreta (an placenta attachment lacking depth), increase after each C-section. Again, the placenta is hunting for the best blood supply and is getting mixed signals because of the uterine scarring from previous C-sections. According to the American College of Obstetriicans and Gynecologists (ACOG), placenta previa and placenta accreta increase simultaneously after each cesarean section. According to ACOG, the risk after the first C-section is 3 percent. After the second C-section, the risk is 11 percent. After the third, it’s 40 percent. After the fourth, it’s 61 percent and after the fifth it’s 67 percent.

The moral to the story is that placental abruption, previa, and accreta, are all disorders of the attachment of the placenta to the uterus and the risk for implantation disorders increase after each additional C-section. A word to the wise consumer. You might want to think seriously about having a vaginal birth after C-section (VBAC).