When a Placenta Tries to Kill a Mother

How C-sections increase the risk of a rare and devastating disorder

It’s 10 a.m. on a Tuesday morning in a hospital conference room, and this not your average birthday planning committee. Here’s the invitation list for the multidisciplinary meeting to plan this Cesarean section:

• Maternal Fetal Medicine (that’s me), the high-risk obstetrics team
• Gynecologic oncology as the premier surgeons of the female pelvis, because we’re planning on performing a hysterectomy immediately after delivering the baby.
• Interventional radiology, because often we will do a small procedure to temporarily block blood flow to the uterus right before the surgery starts.
• Urology, because the bladder is right next to the uterus, and in this case, right next to the placenta, and may become damaged in the course of the surgery.
• Neonatal intensive care, because we are going to need to deliver this baby early in order to minimize the risks to the mother, and so the baby will be going to the NICU.
• Blood bank, because even with all of the above, we usually need to transfuse enormous amounts of blood products to keep the patient alive.
• Anesthesiology, because they’re in charge of keeping the mom and fetus alive during the surgery.
• Nursing, because they need to know everything we plan on doing, and they need to make sure we have the equipment and manpower to do it.
• Critical care, because these patients almost always need an intensive care unit bed after their surgery.

By the end of the list, it’s a pretty big birthday party. But this is not a normal pregnancy, and not a normal delivery. This patient has a placenta that has grown abnormally, called a placenta accreta. Unless we plan this surgery very carefully, this pregnancy could kill her.

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Placentas are, for the most part, simply amazing. They’re one of the first parts of the pregnancy to form—a whole organ that humans make simply for the purpose of nourishing a new human. The placenta lands in the uterus, and grows downward and outward. Complicated structural and immune changes of pregnancy allow the woman’s body to tolerate what, in other circumstances, we would probably perceive as a parasitic invasion.

That’s what happens most of the time, when everything is working properly. Sometimes, however, the placenta doesn’t get the signal to stop growing. It keeps spreading, down and out, through the lining of the uterus. That’s called a placenta accreta. Or the placenta can keep growing through to the muscle wall of the uterus. That’s called a placenta increta. And, horrifyingly, it can penetrate through the uterus, working its way to adjacent organs such as the bladder or bowel. That’s called a placenta percreta.

Most of the time, pregnancies with these problems don’t have symptoms. Long ago, the first sign would often be noted after delivery, when difficulty removing a placenta would be accompanied by enormous, life-threatening amounts of blood loss. These days, with modern imaging techniques, we can often make the diagnosis prenatally.

When the time for delivery arrives, the usual mode of surgery involves a preterm Cesarean section to deliver the baby, immediately followed by the removal of the uterus, with the placenta still attached. So the best-case scenarios end with a preterm baby, a woman who has no future fertility, and a patient who has undergone major surgery. The worst-case scenario involves massive, life-threatening hemorrhage and multiple surgical and postoperative complications. Our job is to give her the best outcome, but prepare for the worst.

There’s an obvious metaphor here, of course, about pregnancy and motherhood, and how they can devour a woman from the inside. But the setup for a placenta accreta often starts long ago, with a prior pregnancy. The other metaphor is that we carry some of the choices that we make forever, and some of them we never heal from entirely.

* * *

Some of the time, placenta accretas just happen. We don’t know why; something between the pregnancy and the woman’s body just goes awry.

But sometimes we do know why. For example, we know that placentas that land on a prior surgical site—most commonly a prior Cesarean section scar— are much more likely to become abnormally implanted. With each Cesarean section, the risk becomes higher. There is something about the way that scars heal that means that the delicate boundary between inside and outside the uterus becomes disrupted and lays the foundation for future abnormal placental growth.

We have long railed at the rising rate of Cesarean section, which now hovers at around 30 percent, because of the procedure’s own immediate risks. But now we’re seeing some of the follow-on ramifications, and they’re pretty scary.

This patient’s own story started when she had one Cesarean section–she’s not entirely sure what happened, but the surgery didn’t seem avoidable.

Then she became pregnant with her second child. I don’t know the details, but maybe this time, her doctor scheduled her for a second Cesarean because the first experience was so scary and she didn't want to repeat it; or because the local hospital was too small to support the resources required (24-hour access to anesthesiologists, for example) to make labors after Cesareans safe.

Or maybe the doctor did talk about it. “I want you to think about a trial of labor after Cesarean,” she might have said. “It has some risks, but it has some benefits. This time you get to decide.”

But our patient would have heard the risks of a natural birth after a C-section, including the 1 percent chance of a possible uterine scar rupture and possible danger to herself and the baby, and she would have gotten spooked. And anyway, another C-section would allow her to, say, have her mom come into town and watch the first baby. So that’s what she chose.

Two years later, the couple decided to try for their third child. And now, she’s here, with a high-risk pregnancy because of a placenta that is in exactly the wrong place. And she had no idea that this could happen.

* * *

Maybe that discussion about her second C-section should have started with this tough question; “How big a family do you think you want to have?” That’s a doozy to hear when you’re six months pregnant, but maybe it’s not fair to omit that repeat Cesarean sections may become a poor choice if you’re thinking of having a large family. Or maybe it should start like this: “There’s no risk-free way out of any pregnancy. Some of the risks we see now. Some of them don’t become clear until future pregnancies. Let’s discuss them and make the right decision for your whole reproductive life.”

The overall risk of a placenta accreta is still very low, and that patient might still have decided that a second Cesarean was the right decision for her. But we need to enter that operating room knowing that we were honest about how complicated it might become; about how we never entirely revert to the body we had before surgery; and how that can mean that sometimes the choices we make today can affect the future in unpredictable ways. We have to at least let the patient consider the fact that we might end up at that conference room planning a very different birthday than we’d like.