What is a Retained Placenta?
Tuesdays with Tony
As I curled up in my usual spot on the seat of Dr. Vurgason’s truck Monday morning, I noticed a distinct, slightly unpleasant, yet oddly familiar odor. It was the scent of placenta. You see, Dr. Vurgason had been out the night before working on removing a retained placenta from a mare that had just given birth to an adorable foal. Curious, and slightly grossed out by the realization of what I was smelling, I started asking Dr. Vurgason all sorts of questions about mares and placentas. Read on to learn why this is something you need to look out for during the immediate post-partum period.
When is a placenta “retained” and why does it matter?
In normal mares, the placenta should pass on its own within 3 hours of the birth of the foal. This recommendation is based on the fact that at birth, the placenta begins to disintegrate almost immediately. That’s 
because the placenta begins to separate from the uterine lining right after birth, and blood flow through the placenta stops. When blood flow stops, a process called autolysis begins. The placenta becomes friable, turns a brownish-green color, and begins to smell quite unpleasant. In short, as soon as the foal is born, the placenta starts to die. Unfortunately, when you leave a dead, decaying, fluid-filled pile of placenta sitting in the uterus for several hours, you end up with a nasty infection.
because the placenta begins to separate from the uterine lining right after birth, and blood flow through the placenta stops. When blood flow stops, a process called autolysis begins. The placenta becomes friable, turns a brownish-green color, and begins to smell quite unpleasant. In short, as soon as the foal is born, the placenta starts to die. Unfortunately, when you leave a dead, decaying, fluid-filled pile of placenta sitting in the uterus for several hours, you end up with a nasty infection. The mare’s post-partum uterus is basically a giant open wound. During this time, there is great opportunity for an infection within the uterus to enter the bloodstream and spread throughout the body. This is called septicemia, or sepsis. And, since horses will be horses, guess what septicemia leads to? You guessed it: laminitis. For this reason, mares with retained placentas will often be treated with broad-spectrum antibiotics, anti-inflammatory medications, and will need to wear ice boots until the threat of laminitis has passed.
Why does this happen?
During a normal delivery, the weight of the foal will begin to pull on the placenta as the foal is born. The umbilical cord attaches to the foal on one end and to the placenta on the other. When the mare stands and the cord breaks, it also gives a good tug on the placenta at the same time. A normal delivery also includes uterine contractions after the foal is born in order to expel the rest of the placenta. This passing of the after-birth is actually considered Stage 3 of labor.
A retained placenta usually happens for one of 2 reasons: either the mare’s uterus doesn’t contract enough, or it contracts too much. If the uterus doesn’t contract enough, or the uterine contractions aren’t strong enough to expel the heavy, blood-filled placenta, it will just sit there indefinitely. The other possibility is that the uterus contracted too much, and in the wrong places. A mare’s uterus is essentially Y-shaped. One arm of the Y would have been the pregnant horn of the uterus. The pregnant horn of the placenta is thin, stretched out, and covers a large surface area. The other arm of the Y would have been the non-pregnant horn of the uterus. The non-pregnant horn of the placenta is thick, narrow, and covers a relatively small surface area. Fun fact: the most common piece of placenta to be retained is the tip of the non-pregnant horn. Too much uterine contraction can actually cause the uterus to grab hold of the thick, narrow non-pregnant horn of the placenta, and refuse to let it go! You see, the attachment between the placenta and the uterus is kind of like Velcro. There are thousands of microscopic, finger-like projections called microvilli that hold the two layers together. Prolonged uterine contractions can in fact cause these microvilli to get stuck within the uterine lining, like a Chinese finger trap.
How do you get a retained placenta out?
I’m so glad you asked, because the technique I’m going to tell you about is super awesome! First of all, the one thing you DON’T want to do is pull on the placenta. In addition, nothing heavier than the weight of the placenta itself should ever be tied to the end of the hanging-out bits. Putting too much traction on the placenta can cause tearing, which leaves fragments of the placenta stuck inside. Even worse, pulling on the placenta can cause uterine prolapse or uterine artery tears, which are definitely life-threatening.
The first thing to try is a single dose of oxytocin. Oxytocin induces strong, rhythmic uterine contractions for a short duration, aimed at pushing the placenta out from within. This takes care of those placentas that are retained because of the first scenario described above: the uterus didn’t contract enough. I’d say about 50% of the time, this works. The mare says, “oh yeah, I forgot about that part!” And out it plops. However, often when the mare has failed to pass her placenta after we gave her 3 hours to do so, there is a reason for it.
So the next step is to call our docs, of course. But you already knew that. One of the methods they might employ to get that stubborn placenta out of there is called the Dutch Technique. In this procedure, the vet makes a small incision in the umbilical vein, just above where it broke away from the foal. Then, a tube is inserted into the vein headed toward the stuck placenta. The other end of this tube is attached to a water hose or pump, and water is steadily pumped into the blood vessel. What this does is distend the vessels throughout the placenta, causing it to separate from the lining of the uterus. After infusing several liters of water, we patiently wait 5 minutes. This part is hard…cats are not particularly patient. After 5 minutes, gentle traction is applied to the placenta. Then, if all goes well, out it plops! It is seriously the coolest thing to watch, trust me.
Well, I hope you learned something from this wise old cat today! Now remember folks, don’t try this at home. Just call one of my docs the moment you suspect there may be a problem.
Until next week,
Tony
Tuesdays with Tony is the official blog of Tony the Office Cat at Springhill Equine Veterinary Clinic in Newberry, Florida. For more information, please call us at (352) 472-1620, visit our website at SpringhillEquine.com, or follow us on Facebook!
