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Video transcript

- [Voiceover] Okay, so I want to start off with a scale. So this is a scale, a time scale. And on this end is before pregnancy, and on this end is after pregnancy, and then in the middle is the 20-week point of pregnancy. And I want to use this scale to show you how different pregnancy related hypertensive disorders are split, because they're split up according to when the hypertension occurs and also according to how severe it is. So starting on this end, let's say a woman has had high blood pressure for several years before she became pregnant, or if she's found out to have high blood pressure before 20 weeks into her pregnancy, then we say that she has chronic, she has chronic or preexisting, chronic or preexisting hypertension. So, her hypertension has nothing to do with pregnancy, because she either had it before she became pregnant, or before the 20-week point into her pregnancy. And this 20-week point is important because before it, sort of in the early stages of pregnancy, pregnancy reduces blood pressure. So if a woman is hypertensive before the 20-week point, then the cause of her hypertension has nothing to do with the pregnancy. Now, if instead she's found to have high blood pressure after the 20-week point in her pregnancy, we say that she has gestational, she has gestational hypertension. I'm just gonna abbreviate hypertension as HTN throughout this video, I'll save a lot of time. Or, hypertension related to her pregnancy, that's what gestational hypertension is. And typically, gestational hypertension, usually, should resolve within 12 weeks of giving birth. If it doesn't, then chances are that the woman probably had high blood pressure before ever becoming pregnant, but that we didn't find it in the earlier stages of pregnancy because of that physiologic lowering of blood pressure that we were talking about that occurs early on in pregnancy. So, I guess you can say that these two conditions, chronic hypertension and gestational hypertension, are sort of the milder forms of hypertension. So now let's talk about the more serious hypertensive disorders, which would have to be preeclampsia. Preeclampsia. Which is kinda spelled weird, preeclampsia and eclampsia. Preeclampsia and eclampsia. So preeclampsia refers to when a woman develops high blood pressure after 20-weeks into the pregnancy. So kinda just like gestational hypertension, but along with a few other features. So in addition to the high blood pressure, there's also protein spilling into the urine, or proteinuria. Proteinuria. So protein in the urine. Or, there's some other form of end organ damage. And I'm gonna go through exactly what that means in just a bit, but there is some other form of end organ damage. Okay, so preeclampsia refers to this constellation of high blood pressure, proteinuria, and end organ damage. And eclampsia is when a woman with preeclampsia develops seizures. Alright, so when a woman with preeclampsia develops seizures, that's called eclampsia. Alright. So it's all good to know the definition of preeclampsia, but why does it happen in the first place? Well, for as much as we don't know about this disease, we're pretty certain that a lot of it has to do with the abnormal development of the blood vessels of the placenta early on in the course of the pregnancy. So the blood vessels in the placenta just don't develop correctly. Now if you remember, during the formation of the placenta, the trophoblast cells of the embryo, which this is the embryo and these green cells on the outside are the trophoblast. The trophoblast invade through the decidua, which is what the endometrium is called during pregnancy. And they also invade through part of the myometrium. And they do this, the trophoblast invade through the decidua so that they can access and infiltrate the spiral arteries, which are the terminal branches of the uterine artery. So they're the arteries that supply the uterus. So they infiltrate the spiral arteries to get access to all of that oxygenated blood that's inside them. And that's how the placenta forms into this bed where blood exchange between mom and fetus can occur. It's because of this first step of the trophoblast invading into the spiral arteries. Now in order for this to happen successfully, I guess you could say two things really have to take place. Two things have to happen. Firstly, the trophoblast have to be pretty aggressive in their infiltration, they really have to dig into the decidua. And secondly, the spiral arteries have to remodel themselves. They have to go from being these narrow, thick-walled blood vessels to sort of being these large, kind of tortuous, vascular channels that allow a large amount of blood to flow through them. So both things have to happen. And we think that preeclampsia occurs when they don't. So the trophoblast do a bad job of digging into the decidua and the spiral arteries just don't change enough to allow for the increased blood flow. So let's sort of take a step back and look at the big picture. If the placenta can't gain good access to the spiral arteries, what that means is a poor oxygen supply to the placenta, which becomes more and more of an issue as the woman gets further into her pregnancy and the fetus and the placenta require increasing amounts of blood and oxygen. So the shortage in oxygen supply makes the surrounding cells of the placenta really angry. That's a really common theme in the human body. When cells don't get enough oxygen, they get angry and they release molecules, usually inflammatory molecules. And that's exactly what happens here. The placenta releases several factors that enter mom's bloodstream. And the factors start altering the way her circulatory system works, specifically the factors start damaging the cells that line the inside of the blood vessels, the endothelial cells. So if this is a blood vessel, we're looking at it head on, it's a cross-section of a blood vessel, we're talking about these cells on the inside. These really thin cells called the endothelial cells that line the inside of the blood vessels. These cells are the target of those factors that are released by the placenta. These are the cells that get damaged. And the damage of the endothelial cells leads to those characteristic signs and symptoms of preeclampsia. So, for example, when the endothelial cells are damaged, they lose the ability to control the tone of the blood vessels. So it becomes harder for the blood vessels to relax and that's what leads to the high blood pressure. The blood vessels aren't able to relax, that's why you end up with hypertension. And the factors released by the placenta also cause the endothelial cells to become more leaky. And these leaky blood vessels allow protein to escape from them. And so when that leakiness occurs in the blood vessels of the kidney, let's say, and protein leaks out from the glomerular capillaries, you end up with protein in your urine, or proteinuria, which is one of the hallmarks of preeclampsia. And throughout the rest of the body, when protein escapes from the blood vessels into the surrounding tissues, right? And if you remember anything about Starling's forces, I know I'm asking you to dig pretty deep with this one, you'll remember that wherever protein goes, water goes. So water follows the protein into the tissues and you end up with edema or swelling throughout the body. So swelling in the face and the hands, and really swelling outside of what you see in normal pregnancy. And the blood vessels in pretty much any organ can be affected, leading to whole body signs and symptoms. So, for example, you can have headaches, you can see headaches, seizures. You can see headaches, seizures, and also visual symptoms. So you can see visual symptoms from the dysfunction of the blood vessels in the brain. You can also have epigastric pain, so pain in kind of that upper middle region of the belly, and elevated liver enzymes. Elevated liver enzymes from dysfunction of the liver. And you can also have fetal growth restriction, so the fetus isn't growing enough from dysfunction of the blood vessels in the placenta. So that's what I meant by organ damage in the beginning of this video. Also, another key point that I'd like to make is that the endothelial cells, when they're damaged, they can release their own factors. So, the factors they release promote clotting, leading to clots throughout the entire body. And as you can imagine, that becomes its own separate, huge issue. Now, the diagnosis of preeclampsia involves looking for all of these features that I just talked about. So in order to make the diagnosis, a woman needs to have high blood pressure, so a systolic blood pressure of more than 140, a diastolic blood pressure more than 90. That's the general definition of hypertension. And she has to have one of the following criteria. She either has to have evidence of proteinuria or she has to have some evidence of end organ damage. So she could have elevated liver enzymes that indicate liver dysfunction, or she could have an increased creatinine, which alludes to kidney damage. Or decreased platelets, which hint clot formation. Any sign of end organ damage will make this diagnosis. And if you've ever spent much time on a ob/gyn floor in a hospital, you know that we screen for this disorder pretty aggressively because preeclampsia can have some really serious complications. It can lead to placental abruption. It can lead to a liver hematoma or rupture. It can also lead to something called disseminated intravascular coagulation, which really just refers to clots forming in the vessels all throughout the body. It can also lead to stroke and even lead to the need for mechanical ventilation. So it's a really serious, it can be a really serious disorder. So how do you cure this seemingly serious disease? Well, really delivery is the only cure. Which makes sense, since the placenta is the source of all of these factors that are damaging mom's vascular system. So removal of the placenta should cure the diesease and it does. Delivery of the placenta always results in complete resolution of the signs and symptoms of preeclampsia. Now of course it's important to consider whether the fetus is mature enough to survive the delivery. So for that reason, if a woman is past 37 weeks into her pregnancy, then we usually procede with delivery if the mom has preeclampsia, regardless of how severe it is. If the pregnancy, however, has not yet reached 37 weeks, then we usually only deliver if the preeclampsia is severe. Now one last point that I'd like to make, eclampsia, or seizures in a woman who has preeclampsia, is one of the most feared complications of preeclampsia and the greatest risk for eclampsia is just before delivery, during labor, and 24 hours after delivery. So for that reason, every woman with preeclampsia is started on magnesium sulfate. So every woman with preeclampsia is started on magnesium sulfate, which is an anti-epileptic agent, or an agent that prevents slash terminates seizures. And the magnesium is given during labor and is continued for 24 hours postpartum, sort of to prevent those seizures from happening. And it's also important to manage the hypertension. You can't just leave the woman with high blood pressures while she's pregnant. So we can use drugs such as hydralazine. Drugs such as hydralazine and labetalol. And labetalol. So hydralazine and labetalol are safe antihypertensives to use in pregnancy. Alright, so those are some details about a pretty feared complication of pregnancy. Preeclampsia.