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




in ancient Egypt women who question whether they were pregnant or not were told to urinate on bags of wheat and barley over the course of several days and if the wheat sprouted the woman was having a girl and the barley sprouted she was having a boy and if neither sprouted she wasn't pregnant so I guess you could say that the question of am i pregnant is as all this time and the craziest thing about that story is that they tested it in the 60s and they found out that it works 70 percent of the time okay so how do we tell if a woman is pregnant in the age of modern medicine so today well there are a few different signs of pregnancy and the signs of pregnancy are divided into three different groups so first there are the presumptive the presumptive the presumptive signs of pregnancy and these are changes that are experienced by the woman that make her think that you might be pregnant and then the second group of signs are the probable signs the probable probable signs of pregnancy which are changes that are seen on physical exam that make the examiner suspect that the woman might be pregnant and then finally there are the positive signs of pregnancy the positive sides of pregnancy are signs that can only and only be explained by pregnancy all right so let's start with the presumptive signs so we're talking about signs that make the woman think she's pregnant and the number-one sign has to be a missed period and the medical term for that is a man Ariha so the medical term for a missed period is amenorrhea and if you've heard enough of these Latin words you may have picked up that putting an A in front of a word means a lack of so this is lack of menses and you know I think it's really important that you understand why the period is missed in pregnancy so really briefly over here you have the uterus right and the uterus has layers but the innermost layer that endometrium is what we're concerned with right now and then off to the side we have the ovary which has lots of different follicles in it and inside each follicle is an egg so really just as a 50,000 foot view of things the whole purpose of the menstrual cycle is to select one of these follicles one of these follicles every menstrual cycle for development so one of these follicles is selected to grow and develop and as it does that as it grows and develops it secretes hormones specifically estradiol so it specifically secretes estradiol which is a type of estrogen and that estradiol acts on the uterus and it causes this inner lining of the uterus the endometrium to proliferate and to become thicker and then in the middle of the menstrual cycle this one mature follicle ruptures and it releases the egg that's inside it and that event that event where the follicle ruptures and releases the egg inside of it is referred to as ovulation after ovulation the egg that's released travels down the fallopian tube hopefully to find a sperm to fertilize it but meanwhile this ruptured follicle that's left behind over here which is now referred to as the corpus luteum right so the corpus luteum takes this sort of waiting period while it's sitting around waiting for the egg to be fertilized to start producing lots of progesterone so progesterone is another hormone that the corpus luteum produces and again the progesterone acts on the endometrium of the uterus to increase the growth of glands and and cause the storage of glycogen and all of this is done to prepare the endometrium to prepare for the implantation of an embryo all right so what does any of this have to do with a period well if that egg that's hanging out over there doesn't get fertilized the corpus luteum recognizes that and it says well I guess there's no reason to prepare this and no metrium for implantation so it stops making progesterone and without the progesterone the endometrium starts to sloth off and that slopping off of endometrium is what's referred to as a period but if instead the egg does become fertilized it will implant into the uterus and when it implants into the uterus it makes this hormone called human called human human chorionic chorionic gonadotropin human chorionic gonadotropin usually it's just referred to as HCG right and human chorionic gonadotropin tells the corpus luteum to stay alive and to keep making progesterone and that progesterone in turn keeps the endometrium alive and healthy so that it doesn't stop off and you don't end up with a period so that is why when an egg becomes for life when you become pregnant you miss a period so that's a lot of information now a lot of the hormones that I just talked about account for the other presumptive signs of pregnancy so nausea and vomiting for example lots of people wonder why do you become so nauseous during pregnancy and one of the reasons for the nausea is progesterone so progesterone is really good at relaxing smooth muscle and that smooth muscle throughout the entire body including the smooth muscle of the GI tract and if you can imagine if the smooth muscle of the GI tract is relaxed instead of contracting food isn't going to make its way down the GI tract like it should it kind of just sits there and it's and and that that piling up of food that stasis of food causes nausea and in addition to all of the estrogen and progesterone the placenta makes a hormone called melanocytes stimulating hormone it's not the most important hormone of pregnancy but it makes this hormone called melanocytes stimulating hormone which does exactly what the name implies it stimulates the melanocytes which are the pigment cells in your skin so hyperpigmentation is not an uncommon sign in pregnancy so darkening of the skin can also occur as assigned in pregnancy and and that could be hyperpigmentation of the face right so the hyperpigmentation of the face is called smile and a lot of people refer to it as the mask of pregnancy so you can see like dark blotchy spots on the face which typically go away within a year after the pregnancy is over but still it can be assigned early on in the pregnancy Linea [ __ ] is another manifestation of that hyperpigmentation so Linea means a line and [ __ ] means black right so it's a dark line that tends to appear down the middle of the abdomen right and and also you can see darkening of the areola of the breasts that's another manifestation of the hyperpigmentation and speaking of the breast many women early on in the pregnancy experience breast tenderness and again not too due to the effects of estrogen and progesterone causing growth of the glands inside the breasts and then somewhere around 12 to 14 weeks into the pregnancy women can start to experience fetal movements for the very first time and they're commonly described as being being flutter like so it feels like a flutter and those movements are referred to as quickening quickening right so quickening so those are the presumptive signs of pregnancy so what about the probable signs of pregnancy well first there's uterine enlargement so so if the examiner feels an enlarged uterus that's a pretty big clue that the woman might be pregnant and of course a positive pregnancy test is another big sign so most pregnancy tests whether they're blood tests or whether they're urine tests detect beta HCG they detect that human chorionic gonadotropin and beta HCG is remember made after the implantation occurs and it can be detected in the urine or in the blood anywhere between 10 to 14 days after conception and I think there tends to be this thought that blood pregnancy tests are way more accurate than urine tests that are done at home but that's not necessarily true so they're a bit a few studies that have shown that a urine pregnancy test is pretty much as accurate as a blood test but it's improper usage or not correctly following instructions at home that tend to result in an inaccurate home pregnancy test and you might be wondering why a positive pregnancy test isn't a positive sign of pregnancy why is it a probable sign of pregnancy and it's because you can actually have a false positive pregnancy test because there are certain types of cancer that also produce HCG so as you can imagine that would also lead to a positive pregnancy test in the absence of a pregnancy all right now as far as the remainder of the probable signs of pregnancy keep in mind that during pregnancy the blood flow to the entire reproductive tract including the URIs and the vagina drastically increases there are more blood vessels growing in these organs and more moms blood is being directed this way and that makes these tissues really quite loose and swollen and elastic right so for example the tip of the cervix become soft and swollen and that can be seen or it can be felt by an examiner and that and that softening of the tip of the cervix is referred to as good else sign referred to as good else sign so it's something that an examiner can see that would sort of indicate that the woman might be pregnant and all of those blood vessels give the cervix and the vagina a violet bluish color which again can be seen during an exam and that's referred to as Chadwicks sign so refers to the bluish tinge of the vagina and the cervix and eventually actually an examiner can feel the presence of the fetus so there is this maneuver where the examiner can insert their finger through the vagina and gently tap upwards which causes the fetus to rise right and then the fetus sinks and then the examiner feels a gentle tap back on their finger and that technique of gently sort of bouncing the floating fetus is referred to as Belote meant it's referred to as as balut balut mint so those are the probable signs of pregnancy leaving us with the positive signs of pregnancy which are signs that can only only be explained by pregnancy so they include visualizing the fetus so direct visualization of the fetus either through ultrasound x-ray right also hearing fetal heart tones hearing fetal heart tones and feeling fetal movements feeling fetal movement so visualizing the fetus hearing the fetal heart tones and feeling fetal movement are signs that are absolutely diagnostic of pregnancy they can't be explained by anything else alright so those are some of the different ways we can tell if a woman is pregnant which just shows you that we've we've come a pretty far away from the days of urinating on bags of barley and wheat