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Preterm labor

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] Let's start out with some definitions. So, preterm labor refers to delivery that occurs too early. and by that, we mean before 37 completed weeks of pregnancy. So, delivery that occurs before 37 completed weeks of pregnancy. And a normal term pregnancy, right, so, a full term pregnancy is anywhere from 37 to 41 weeks long. And so, preterm is anything short of 37 to 41 weeks. And I wanna highlight that this is a really important topic to discuss because preterm birth is the number one cause, the number one cause of neonatal mortality. So, it's the leading cause of death in the first 28 days of the baby's life. And, really, even in those babies who do survive, they're at risk of developing long term issues, so, neurodevelopmental deficits, for example, jumps out to the forefront of the mind, such as cerebral palsy, impaired learning, visual issues, so, it's a really big issue. And you can probably imagine the risk of death and the risk of these complications decreases the further along the pregnancy is at the time of birth. So, a 36 week old premature baby will probably fair better than a 30 week old premature baby, for example. And with the same token, a higher birth weight in a premature baby is also associated with less complications with a better outcome. So, what causes preterm labor to occur? I mean, the pregnant body knows that the baby needs to be kept inside for 37 to 41 weeks, so, why would it initiate labor earlier than that? Well, we kind of break up the causes of preterm labor into four groups, so, four major causes. The first major cause is stress. Whether that's major physical stress or psychological stress such as with anxiety or depression, and there's thought that the stress, whether the physical stress or the psychological stress, activates the HPA axis. So, the stress activates the HPA axis, which stands for the hypothalamic-pituitary-adrenal axis in the mom. And this long named axis is basically the stress axis of the body. And when it's activated, stress hormones get released. So, when the HPA axis is activated, the stress hormones get released and the stress hormones are what initiate the preterm labor. And this idea that stress can actually induce premature labor has been validated. It's actually been shown that women who have symptoms of depression, for example, have twice the risk of going into preterm labor compared to woman who don't have those symptoms. And really, the same stands true for the opposite side of things, for the other side of things. So, if the fetus experiences any stress, it's associated with an even higher risk of preterm labor. So, in this case, we're talking about stresses such as damage to the fetal blood vessels, or improper formation of the blood vessels in the placenta, like what you see with preeclampsia. So, when we're talking about fetal stress, we're talking about issues that reduce the oxygen nutrient delivery to the baby that induce stress in the baby. Alright. So, this is the first mechanism of preterm labor, so, stress induced preterm labor. The second major cause of preterm labor is inflammation which can be the result of some inflammatory condition, certainly, or inflammation from infection. So, anything ranging from urinary tract infections to dental infections, or infections of the actual fetal membranes, these are all things that can lead to preterm labor. And in addition to causing inflammation, bacteria can actually cause preterm labor through another mechanism where they create several different enzymes that can actually degrade, they can actually break down the fetal membranes which can induce labor. So, inflammation, whether it's through an inflammatory condition or through infection can cause preterm labor. Now, the third major cause of preterm labor relates to placental abruption. Placental abruption, which is when you have bleeding that occurs between the placenta and the uterine wall because of some pathology, some irregularity that makes the uterine blood vessels more fragile and more prone to rupture. And it kind of makes sense how this would lead to preterm labor because in response to this bleeding that's occurring between the placenta and the uterine wall, the uterus does what it knows best, it starts to contract. Because this contraction of the uterus squeezes down and clamps down on the blood vessels that are traveling though the wall of the uterus. So, great, that slows down the bleeding. But, of course, a side effect of all of that contraction is the induction of labor. So, that's how you get preterm labor with placental abruption. And finally, the last major cause of preterm labor is an abnormality, some abnormality in uterine distension. So, the uterus is more distended than it normally would be at that point in the pregnancy. And that stretching of the uterus, that stretching of the myometrium of the uterus, muscular layer of the uterus, sort of tricks the body into thinking that the pregnancy is further along than it actually is. And a couple of things that can cause the uterus to be more distended than usual include multiple gestation, so, having twins, triplets, quadruplets, et cetera, or polyhydramnios. So, polyhydramnios is another thing that can lead to uterine distension, and polyhydramnios refers to when there's too much amniotic fluid. So, that can also do it. And I guess in this category, you could also talk about abnormalities with the cervix. So, the cervix can be too dilated or too effaced, so, too thin in the absence of labor. And we refer to that as cervical insufficiency. Cervical insufficiency. So, basically, that the cervix isn't staying shut, making it more likely for preterm labor to occur. Okay. So, how do we diagnose preterm labor? Well, you start off by looking for signs and symptoms of labor, right? Regular labor, such as uterine contractions. Now, remember that irregular uterine contractions occur at all stages of pregnancy. They're called Braxton Hicks contractions or sometimes, they're called practice contractions. Right, and they occur all throughout pregnancy. So, it's really important to distinguish those Braxton Hicks contractions, so, those practice contractions from true labor contractions. And in labor, what we're looking for is contractions that are more regular, more frequent, and more intense. And those uterine contractions have to be accompanied by cervical change. So, the cervix has to become more effaced. So, more thinned out, and it has to become more dilated, so, it has to spread apart. And we assess for that cervical change by doing a speculum exam. So, we insert a speculum through the vagina and look inside. And also, while we're looking inside, we also look for cervical, we also, while we're looking for cervical change, we also look to see whether the fetal membranes are intact or whether they ruptured because if the fetal membranes have ruptured, which is commonly referred to as the water breaking, or the water bag breaking, it's more likely that the woman is in true labor rather than in false labor. Now, in women who are less than 34 weeks along in their pregnancy, and whom were really uncertain of whether they're in labor or not, we tend to get a transvaginal ultrasound. So, a transvaginal ultrasound is when you take an ultrasound probe, it's a long probe, and you insert it through the vagina so you can get a really good picture of what's going on at the level of the cervix and the rest of the uterus. And we do the transvaginal ultrasound to determine what the cervical length is, so, we wanna see how long the cervix is because a short cervix, a short cervical length before 32 weeks into pregnancy is a really good predictor for preterm labor. So, having a short cervix before 32 weeks into the pregnancy is a really good predictor of preterm labor. And, of course, the ultrasound gives us lots of other information like whether there are any maternal or fetal, and atomic abnormalities, it can tell us the position of the fetus, if there's enough amniotic fluid, and it also allows us to estimate what the fetal weight is. And all this information is critical in determining the potential outcomes of the preterm birth, and it helps us to sort of counsel the parents on what the potential outcomes can be. Alright, so, the next step after confirming that the mom is preterm labor is to manage it. So, in all women who are less than 34 weeks into their pregnancy, the very first step is always to administer a dose of steroids. Usually betamethasone. So, betamethasone. Betamethasone is a type of steroid, right? And the administration of one dose of betamethasone has been consistently shown to reduce fetal mortality and complications from the preterm birth. And along with that betamethasone, the mom also receives a tocolytic agent. So, she'll also get a tocolytic agent, which is an agent, it's a medication that relaxes the uterus, so, it attempts to delay the delivery. And we give the it tocolytic agents for up to 48 hours with the hope that we can delay the delivery until the steroids have had a chance to take effect. Now, in addition, in women who are delivering even earlier on, so, before 32 weeks, anywhere between 24 to 32 weeks into their pregnancy, we also give a dose of magnesium sulfate. So, in addition to everything else, we give a dose of magnesium sulfate which has a protective effect on the brain of the fetus, so, it helps to prevent cerebral palsy and other neurologic issues that tend to occur in severely premature babies. So, I guess that leaves us with, is there anything you can do to prevent preterm labor? And the answer is perhaps. So, the number one risk factor for preterm labor is having a history of preterm labor in a previous pregnancy. And in these women who are at really high risk, right, so, if they've had a history of a preterm pregnancy, there's a good body of evidence to support the use of progesterone supplements throughout the pregnancy. So, giving it to them throughout the pregnancy to reduce the risk of preterm labor. And while there are several things that put a woman at risk for going into preterm labor, there are a couple of modifiable risk factors, so, risk factors sort of in the control of the woman that she can eliminate to reduce the risk of preterm labor. So, things such as cigarette smoking, cocaine use, right, so, avoiding those substances can also help to reduce the risk of preterm labor.