Pregnancy and pregnancy complications
- [Voiceover] One of the most annoying things ever has to be when you're putting on a screen protector on a phone and you notice a bubble in it. You guys know what I'm talking about. It happens to pretty much all of us. There is this bubble where the screen protector isn't touching the screen of the phone and so the screen protector can't do its job. It turns out this is really similar to what a placental abruption is. So, you've got the uterus and there's the fetus inside the uterus, and there's a placenta which, remember, is this pool of blood that has the oxygen and the nutrients that the fetus needs to grow and thrive. And the pool of blood is supplied by uterine arteries, which are juicy and plump during pregnancy. Now there aren't only three arteries and they aren't really this big but this is drawn this way for simplification. So what I've tried to show with this diagram is that the placenta is really nicely sealed to the wall of the uterus, and that's essential for the placenta to do its job. But what can happen sometimes for a variety of different reasons is that these uterine arteries here can tear, they can actually rupture, and the blood that's inside them will flow out and start to build up between the uterus and the placenta, like this. So this is kind of like that screen protector bubble that we were talking about earlier. And at this point where the placenta isn't attached to the uterus anymore, the placenta isn't receiving the oxygenated and the nutrient-rich blood anymore so it can't do its job of turning it around and providing it to the fetus. So it turns out that this accumulation of blood can stay small, it can stay limited. Or the bleeding can continue and the pressure from that blood can dissect through or it can tear through the seal between the placenta and the wall of the uterus, causing the placenta to separate from the wall of the uterus. And with that, some of the blood can leak through the vagina, which is usually how this condition is noticed. The mom will have some vaginal bleeding. Now, before we go any further let's talk a little bit about about some nomenclature. So, when there's only a little accumulation of blood and it's hidden behind the placenta it's called the concealed abruption. And, as you can imagine, you don't get any vaginal bleeding with a concealed abruption, right? It's pretty much trapped behind, the blood is trapped behind the placenta. But when the blood has torn through the entire seal and the placenta is completely separated from the uterus it's called a complete abruption. So, getting back to some of the symptoms of abruption, the first is vaginal bleeding. Vaginal bleeding that occurs late in the course of the pregnancy, specifically after the 20-week mark, and that's referred to as antepartum, as antepartum bleeding. And there are two main causes of antepartum bleeding. One is placenta previa, which presents with painless antepartum bleeding. And the second is placental abruption, which presents with painful, very painful antepartum bleeding because, as you can probably imagine, the placenta shearing apart from the wall of the uterus to which it was pretty tightly attached is a painful process. Now, in addition to painful vaginal bleeding, the mom, the patient, also experiences uterine contractions. And to understand why this occurs, why you experience uterine contractions, you have to understand that the uterus is first and foremost a muscle, and in this situation where blood is leaking from the uterine arteries, the uterus tries to control the bleeding by doing what it knows best and that is to contract. And the goal of these contractions is to squeeze down on these arteries that pass through the wall of the uterus to limit the amount of blood flowing through them. And while that's a pretty effective way of controlling the bleeding, it also has an unwanted side effect of sometimes pushing out the baby. That is to say that these uterine contractions can sometimes lead to premature labor. And while we're talking about the symptoms of placental abruption, let's not forget what happens to the baby. With the placenta being separated from it's blood supply, the fetus isn't receiving the oxygen that it needs, so the fetus can become asphyxiated, and it can show with concerning heart tracings. So, usually that's referred to as nonreassuring fetal heart tracing, which is abbreviated this way. And usually, this constellation of symptoms is how placental abruption presents. And it's really important to know and to understand these symptoms, and it's because the diagnosis of placental abruption is primarily a clinical diagnosis. So sure, you can try to image the uterus and the placenta but during pregnancy you're pretty much restricted to the use of ultrasound because of the concern for harming the fetus with other imaging modalities. And on ultrasound, blood, especially fresh blood, and the placenta have a very similar appearance. So that can make it difficult to diagnose an abruption with ultrasound. That's not to say that it can't be done, just that it can be difficult at times. Now, in the case that you do make a diagnosis of abruption, deciding what the next step is can be pretty complicated. On one extreme end of the spectrum, where mom and baby are both unstable, delivery is usually the answer. Delivery is also usually chosen if the baby is past 34, 36 weeks and is healthy enough to survive outside the uterus. On the other end of the spectrum, if the abruption is really minor and both mom and baby are looking good and the baby is too young to survie outside the womb alone, we can usually monitor both mom and baby until delivery is a safe option. So, after having discussed all those features of abruption, let's consider some of the causes of abruption. Remember that the end point of all these causes has to be the tearing or the rupture of the uterine arteries that's the ultimate cause of placental abruption. So, the one cause that always jumps out to me is trauma. I always remember trauma, and I try to do this animation thing to show how trauma causes abruption. So, if a pregnant woman is in a car accident or any traumatic event really, the uterus stays fixed, it doesn't move, because after all, it's attached to your skeleton, it's attached to other organs. But, that's not the case for the placenta and the baby. So any trauma or any mechanical event can cause the placenta to shear away, to stretch and rupture these uterine arteries, which leads to bleeding and abruption. Now, as much as I tend to remember trauma as being the main cause of abruption, and you probably will too, trauma turns out to be a pretty uncommon cause. Most abruptions are actually due to chronic processes, long-term processes, that affect how blood vessels form early on in the course of the pregnancy. So causes such as hypertension or high blood pressure, smoking or cocaine use, these conditions cause diseased blood vessels to form. Blood vessels that are fragile, that are easily broken, right? That can lead to placental abruption. So, in a nutshell, that is placental abruption.