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Blood conditions in pregnancy

Visit us (http://www.khanacademy.org/science/healthcare-and-medicine) for health and medicine content or (http://www.khanacademy.org/test-prep/mcat) for MCAT related content. These videos do not provide medical advice and are for informational purposes only. The videos are not intended to be a substitute for professional medical advice, diagnosis or treatment. Always seek the advice of a qualified health provider with any questions you may have regarding a medical condition. Never disregard professional medical advice or delay in seeking it because of something you have read or seen in any Khan Academy video. Created by Nauroz Syed.

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Video transcript

- [Voiceover] One of the most amazing moments for a woman is when she finds out she's pregnant, or I guess I should say when her brain finds out because her body is already aware of it from several weeks before. So much so that by the time a woman finds out that she's about to be a mom, her body has already undergone several changes to prepare for that growing baby. One of the first and most important changes that the body makes is that it realizes that it needs more oxygen, which means that it needs more red blood cells to carry the oxygen within the blood. And in order to do that, the level of a hormone called Erythropoietin have to increase. And Erythropoietin is this hormone that stimulates the bone marrow to increase production of red blood cells. And those levels don't increase by just a little. They increase up to 50%. In fact, if the pregnant body could have its way with things, the amount of red blood cells would increase by something like 20% to 30% over the course of a pregnancy. But what actually ends up happening a lot of the time in pregnancy, is that women become anemic, so the hemoglobin and the hematocrit values, which are measures of the amount of red blood cells you have in the blood, decrease. Instead of increasing, they decrease. And that can happen for a couple of different reasons. The first reason is something that happens in normal, pregnant women, and that is that the plasma volume, which plasma is like the liquid component of blood, the plasma volume increases more than the red blood cell mass. So even though the amount of red blood cells is increasing, the concentration of red blood cells in the blood is decreasing. Does that make sense? So that's the first thing. And it's called a physiologic anemia, because it's a part of normal pregnancy physiology. Now, another thing that can happen is a true anemia, or a pathological process, not a physiological process, but a pathological process, in which there is an actual decrease in the number of red blood cells. So here we're not talking about concentration, we're talking about a decrease in the actual number of red blood cells. Most commonly, that anemia, the true anemia, is due to a shortage of iron in the body. So iron is used to make hemoglobin, it's an essential part of hemoglobin, and red blood cells are basically packets of hemoglobin. So no iron means no red blood cells. It's kind of like, if you're going to go make chocolate chip cookies and you want to make, let's say, 100 of them, and you have enough of all of the ingredients to make 100 cookies, but you only have enough chocolate chips to make 80 cookies. So guess what? You're gonna end up with only 80 chocolate chip cookies. So why the shortage of iron? Why is there a shortage of iron in pregnancy? Well, these women, the pregnant women, are by definition, women of reproductive age, right? So they were probably menstruating before becoming pregnant, and that blood loss that occurs with each menstrual cycle claims some of the body's iron stores. So, that's one cause for the iron shortage in pregnancy. Another cause is that, in trying to make it's own red blood cells, the fetus claims some of mom's iron stores. Now, iron deficiency is, by far, the most common cause of anemia in pregnancy. So much so, that if a woman is a pregnant woman is found to be anemic, she is usually treated with iron supplementation, and only if that doesn't resolve the anemia, if the supplementation doesn't resolve the anemia, do we go looking for another cause. So speaking of other causes, it's worth mentioned that folic acid deficiency, so, deficiency of folic acid, right? can also, less commonly, cause anemia in pregnancy, as can other causes, all the other regular causes of anemia. And something that happens particularly in pregnancy is that the lifespan of a red blood cell decreases, so the red blood cell doesn't quite live to be 120-days old before dying, and this further contributes to the anemia that we tend to see in pregnancy. So, I want to make the point that anemia isn't a problem that's unique to pregnant women, and you probably already know that, but anemia does have some unique implications in pregnancy that it doesn't have in other people. For example, it can lead to things, such as, a reduction in amniotic fluid levels in the fetus. It can cause concerning fetal heart tones or fetal heart tracings. It can lead to spontaneous abortion, low birth weight of the fetus, and even death of the fetus, so it can be a pretty serious problem in pregnancy. Now, there's another important change that occurs in the blood system of the mom during pregnancy, and that is that pregnancy is a hypercoagulable state, so that is to say that the clotting mechanisms in blood are running in overdrive during pregnancy, so blood clots really easily, and this is primarily because in pregnancy, there is an increase in the production of clotting factors. Factors such as thombrin and fibrinogen and other clotting factors are made more. And there is a lot of thought that perhaps this occurs to protect the mother from excessive bleeding during delivery, especially the bleeding that occurs when the placenta separates from the uterus. So maybe this is all meant to be protective? The problem is, is that sometimes you can have too much of a good thing, and you end up with blood clots, most commonly in the deep veins of the legs. And some of that actually has to do with the fact that the enlarging uterus puts pressure on the inferior vena cava and the veins of the legs. And that causes blood to pull in the lower extremities, which is actually why pregnant ladies almost always complain of swollen legs. Anyways, this pooling of blood in the legs can lead to blood clots, and those blood clots are called deep vein thrombosis. Thrombosis just means clot. So, in fact, the risk of having a deep vein thrombosis is increased by five-fold in pregnancy and it's important to know because the clot in the legs can break off and it can travel to the lungs leading to a pulmonary embolus, in up to 40% of cases in which you have DVT, which is dangerous and potentially fatal to the mom. So, when the presence of a DVT or any clot or thromboembolism, for that matter, is confirmed, the woman is put on anticoagulant therapy right away. So those are just a couple of the very important changes that occur in the blood system of a pregnant woman.