If you're seeing this message, it means we're having trouble loading external resources on our website.

如果你被网页过滤器挡住,请确保域名*.kastatic.org*.kasandbox.org 没有被阻止.



访问我们的健康和医药内容(http://www.khanacademy.org/science/healthcare-and-medicine)或MCAT相关内容(http://www.khanacademy.org/test-prep/mcat) 。这些视频不提供医疗建议,仅供教学目的。这些视频不能替代专业医学建议、诊断或治疗。如有情况及疑问,请寻找正规医疗机构。请勿因可汗学院视频内容,无视医嘱,延误病情。 Nauroz Syed 创建




I thought the movies taught me everything I needed to know about labor and delivery the water breaks mom yells everyone rushes into the hospital and after a few breathing exercises and tours re really hard and loud pushes the baby arrives what reality couldn't be further from that for one thing most of the time labor is preceded by few signs that tell the mom that the baby is about to come one of those signs is lightning one of those signs that tells the mom that the baby is about to make his or her debut is lightning or well people like to call the drop and what it refers to is the baby's head engaging with and sort of settling into moms pelvis which the mom can feel it feels like the baby is sitting lower in the abdomen and and this is my sort of diagram depicting that so I don't know if you can tell but this is the pelvis and this here this here is the baby and you can see that the baby's head is sort of nestled into and settled into mom's pelvis and that's called lightning another one of those signs that tells mom that baby is about to come is Braxton Hicks contractions they're called Braxton Hicks contractions sometimes called practice contractions and that's exactly what they are they're uterine contractions that occur as early as the first trimester but unlike real labor contractions there they're infrequent they're irregular and they don't occur with a pattern so as delivery approaches Braxton Hicks contractions tend to become more frequent and they tend to become more uncomfortable and then another big sign of impending labor is loss of the mucus plug which the mucus plug is the mucus that seals the opening to the cervix so it seals the endocervical canal the canal that's inside the cervix and when the cervix loosens up and it dilates during labor the plug falls out and sometimes when that mucus plug is blood-tinged it's referred to as the bloody show it's referred to as the bloody bloody show I always wondered that was the bloody show okay so those are some of the signs of impending labor but what on earth is labor well labor is when you have regular uterine contractions that lead to changes in the cervix and the passage of the baby so the contractions have to be regular they have to be patterned and they have to lead to some change in the cervix and that's what labor is and we split labor up into three distinct stages with each stage kind of having its own goal so there's the first stage of labor right so there the first stage of labor the second stage of labor second stage of labor and the third stage of labor and we're gonna go through each of these stages independently starting with the first stage of labor which is the longest stage of labor and the first stage of labor is all about the cervix becoming fully dilated and what that means what it means for the cervix to become fully dilated is that the cervix goes from being thick and completely shut to thinning out and opening up ten centimeters ten centimeters is what we call completely dilated and that's a lot of change right so it doesn't happen all at once instead it happens in three distinct phases so the first stage of labor has three phases to it and the first of those phases is called the latent phase the latent phase right and during the latent phase contractions become stronger they become more frequent and more regular and most of what's happening during this phase is the thinning or the effacement of the cervix so that looks something like this you can see the cervix is becoming thinner right not too much dilatation is occurring in fact at most the cervix will become 3 centimeters dilated max during this phase so this phase the latent phase is actually the most variable phase from woman to woman so for a woman who's had kids before we expect it to last anywhere from 10 twelve hours but for a woman who's having her very first baby it can take as long as 20 hours so that's a lot of variability okay so we hope that by the end of the latent phase the cervix is maximally thinned out so that during the next phase which is called the active phase active phase we can focus on the dilatation of the cervix right so during the active phase the cervix goes from being two to three centimeters dilated to becoming eight to nine centimeters dilated and that's that's sort of looks like this right so you can see that the cervix is becoming dilated or the space is increasing and this phase is what you can call the most predictable phase of labor it's so predictable that we measure its rate by that I mean that in a first-time mom the cervix has to dilate at least one point two centimeters per hour and that's in a first-time mom and for a mom who's had multiple kids in the past the cervix has to dilate quicker so at least one point five centimeters an hour it's that predictable that predictable that we have this rate for it so much so that if the cervix isn't dilating at the rate that we expected to we get really concerned so that leaves us with the last phase which is called the deceleration the celebration phase which some people like to call the transition transition so the deceleration phase and transition are two interchangeable terms for this phase and during this phase the cervix continues to dilate but more slowly than it did in the active phase in some women this isn't as much as separate phase as it is kind of an extension of the active phase so it kind of blends in with the previous phase also the baby passes lower into the pelvis and deeper into the birth canal during this phase okay so now we have a fully effaced right so fully thinned out and a fully dilated cervix second stage of Labor marks the period between when you have a fully dilated cervix to the delivery of the baby for a lot of people this is what's known as the pushing stage and usually usually this should take less than an hour in a woman who's done it before in less than two hours in a first-time mom but keep in mind that the use of of something like an epidural can prolong this stage so it slows things down okay and then finally finally the final stage is stage three which is the period between the delivery of the baby and the delivery of the placenta and this shouldn't take any longer than thirty minutes so I hope that this has taken out some of the mystery out of what normally occurs during labor but what about when things don't occur normally what about when labor isn't progressing as quickly or as effectively as it should well if that's the case then we need to evaluate the three P's so if neighbor isn't progressing the way that it should we evaluate the three P's the first P is powers right the first P is powers the second P is passenger passenger powers passenger and the last P is passage so the three P's powers passenger and passages is what we sort of evaluate if labor isn't going the way that it should if it's abnormal so powers the first P refers to uterine contractions or more specifically to the force that's generated by the uterine muscles when they contract so if there's an abnormality during labor we have to ask ourselves is it because the uterine contractions aren't occurring frequently enough are they are they not lasting long enough or maybe are they not strong enough and we can assess that simply through observation so typically we think that during active labor we should have about three to five contractions every ten minutes right so we should have three to five contractions every 10 minutes with each contraction lasting somewhere between forty and six these seconds and each contraction being strong enough that the uterus feels firm when you palpate it when you touch it or if you prefer to use more objective measure there are these devices called intrauterine pressure catheters that you can actually insert through the vagina and onto the uterus that will give you a numerical measure to a more objective measure of how strong each contraction is either way we know that contractions during labor have to be adequately frequent and adequately strong to achieve labor and if they're not we can use a drug such as oxytocin so there's this drug called oxytocin which causes the uterus to contract to sort of help us along and you you also have to think about the second contributor to Powers and that's the bearing down efforts of the mom and you have to think about if those are strong enough if the mom is sort of pushing effectively and strongly enough okay so if powers isn't the problem then we need to consider the second P passenger which of the passengers of course the fetus so some things to consider about the fetus include what it's orientation is so whether the head the feet or the shoulders are delivering first right because that can affect thing we have to consider whether the head is flexed or whether its extended and of course how big the fetuses head is is also important to think about if you're having any abnormality in labor and then finally there's a last P or passage which refers to mom's sort of bony pelvis and the soft tissues of the birth canal so the cervix and the pelvic floor muscles right so abnormal labor could be the result of something we call cephalo something we call us a fallow the fallow pelvic fallow pelvic disproportion so abnormal labor can be the result of a low pelvic and disproportion and so fallow means head pelvic refers to pelvis right so we're talking about a disproportion between the baby's head and the moms pelvis so basically the baby's head can't fit through mom's pelvis either because babies too big or mom's pelvis to small in either case since you really can't change either variable c-section tends to be the only sort of treatment for this problem all right so that's a brief very brief overview of labor hopefully the next time you see a Hollywood delivery you'll appreciate exactly how much they're leaving out