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SAL KHAN: I'm here with the Dr. Laura Bachrach at Stanford Medical School. And what are we going to talk about? DR. LAURA BACHRACH: We're going to talk about normal and abnormal growth in children. SAL KHAN: Fascinating. DR. LAURA BACHRACH: So this is an important concern. Parents really worry if their child is growing normally. And physicians worry about this too, because the change in height is an important barometer of how the child is doing overall, in terms of health. So to begin to assess the child's growth pattern, we have to think about what are the determinants of where the child should be on the growth curve. The number one most important determinant, of course, is genetics. Short parents are more likely to have short children and vice versa. SAL KHAN: And that's true even when a child is young, because sometimes I've seen the opposite. So people who are petite have large children and all the rest. But it is true that, if someone is large, they're more likely to have large children, even infants and toddlers. DR. LAURA BACHRACH: You've hit upon a really important issue that's shown here in this slide. The size of a baby at birth isn't necessarily going to reflect the genetics. There are babies that are born small, because mother didn't have prenatal care. Mother was a smoker, other factors that compromise the growth of the child. And those babies can be born small for their gestational age. During the first two to three years of life, they have a chance to catch up on the curve and reach what's called their genetic potential. SAL KHAN: So let's just make sure. I want to make sure. I've seen these curves before, when I went to visit a pediatrician, even I remember this when I used to visit the pediatrician, which I did maybe a little too long. So this axis right over here is age. DR. LAURA BACHRACH: In months. SAL KHAN: In months-- so this is right here birth. This is birth. So if a baby is born at-- I don't know. This is the weight right over here. So if a baby is born at five pounds-- is this in pounds? This is kilograms. OK, so five pounds is right over. Is that right? Yeah, five pounds would be right over here. So this would be a baby born at five pounds. DR. LAURA BACHRACH: Right. And I'm talking more here, during this growth lecture, about the height or length of the baby, throughout babyhood and childhood. But let's say, the baby were born light in weight and short in length. SAL KHAN: So maybe 18 inches right here would be a short length. DR. LAURA BACHRACH: Right, and let's say, that baby was small because his mother had issues during the pregnancy. SAL KHAN: Is it always the case that the baby will be small because of issues? DR. LAURA BACHRACH: No. The bottom line is that genetics plays less of a part in the size of the baby at birth than it will later on in childhood. SAL KHAN: All right, it makes sense. DR. LAURA BACHRACH: So to come back to your point, you'll meet parents whose baby seem to be larger or smaller than they are. But by age three the child should be-- SAL KHAN: Hold on one second. Let me just close this. OK. DR. LAURA BACHRACH: By age three, the child should be in his or her genetic groove, if you will. SAL KHAN: I see. DR. LAURA BACHRACH: So there can be movement on the growth curve in the first two to three years of life. There can be catch-up growth, where the child, who was small, let's say, moves from below the curve up to the 50th percentile, by age 24 months. SAL KHAN: So this would be a child who does something like this. DR. LAURA BACHRACH: Exactly, exactly. And you can have the converse, where you have a very big baby. Let's say, mother had uncontrolled diabetes, and the baby was born very large. That baby can have catch-down growth, to the 50th percentile. By the age of three, certainly movement across percentiles is considered to be abnormal and warrants an investigation. SAL KHAN: So you really can predict someone's even adult height, based on where they at three? DR. LAURA BACHRACH: A general rule of thumb is, that by age 2 and 1/2 to 3, the child is in their genetic groove. SAL KHAN: Really? Oh, wow. I didn't realize that quickly you can kind of-- so if a child, at age three or four, is in the 25th percentile in height, it's unlikely that they're going to be in the NBA? DR. LAURA BACHRACH: In general, that's true. There are a few exceptions. There are late bloomers, what we call a constitutional delay of growth. But a general rule would be, what percentile you are by the age of two or three is pretty much where you're going to track, if all things are going normally. SAL KHAN: Wow, I never realized that it was that soon. DR. LAURA BACHRACH: And genetics is an important determinant as I said. We can actually do a calculation of where we think a child should end up, the so-called mid-parental height, which we are going to talk about later. So genetics is the critical factor. But whether or not you reach your genetic potential means that the cards have to be lined up appropriately. So the cards that are important for achieving your genetic potentials, first of all, number one-- normal amounts of hormones that are important for growing. And those are thyroid and growth hormone, to a large extent. A second factor, of course, is adequate nutrition. And we think worldwide of children who are undernourished, who don't look anywhere near their age, in terms of height, because they're so undernourished. It really cramps their style. SAL KHAN: And you see the reverse of that. I mean, I don't know what I am officially. I was born here. My parents weren't. So I'm what, first generation or second generation. But you see that in that, is that you see a lot of people in my generation are much taller than their parents, because their parents were probably malnourished in some way. DR. LAURA BACHRACH: Certainly, there can be a secular trend, where the children get taller than the parents, if the children have a different environment. The other thing we notice about nutrition in our country is the over-nutrition of our children. And what happens with obesity is that children may grow faster, in terms of both weight and height for their age. They don't end up taller in the long run. But they move ahead more quickly through the maturation process. SAL KHAN: I see. I didn't know. OK, it can accelerate. DR. LAURA BACHRACH: Exactly. SAL KHAN: I never realized that. That's fascinating. DR. LAURA BACHRACH: And then we think about psychosocial factors. There literally is a situation where infants can be deprived of parental love and support, and you see something dwarfing there. In a teenager, we see problems with eating disorders, that's a cross between nutrition and a psychological problem. So psychosocial factors play a role as well. SAL KHAN: So they've shown, or it's been seen that it's noticeable changes in physical development, based on, I guess, attention and love. DR. LAURA BACHRACH: Yes, there's actually a syndrome called psychosocial dwarfism, where you can actually see a slow down in growing without adequate interpersonal support. SAL KHAN: Wow, that's fascinating. DR. LAURA BACHRACH: So the issue is, when do you need to worry about a child's growth pattern? In order to interpret that, you have to understand about the variability in growth. In the first two to three years of life, children grow much more quickly than they will later on. By the age of three, until they hit puberty, children should grow two inches a year. SAL KHAN: Two inches a year, this is from the ages of-- DR. LAURA BACHRACH: After they're out of toddlerhood until they hit puberty. SAL KHAN: So this is like three to puberty. DR. LAURA BACHRACH: Exactly, exactly. But when kids will hit puberty is going to be variable. And so that's an issue. If children are growing at a normal rate, it's not necessary to memorize the inches per year. Children will track along the growth curve. And if we can turn to the next slide or next graph, this is a graph for what we use for older children, after the age of 2 up until they're 18. This is the curve that we use. Now, beyond the age of two, I said to you, it's not normal for children to necessarily cross percentiles. So if, for example, you have a child who is tracking along the fifth percentile every year, growing their two inches a year. SAL KHAN: This is the fifth down here? DR. LAURA BACHRACH: Right, the lower line there. They're moving along, steadily, steadily, steadily. That child has a more reassuring growth curve than one, for example, who as a five-year-old had been at the top of the curve. SAL KHAN: Right, a five-year-old. So five-year-old is right there. DR. LAURA BACHRACH: And then the next year is on the 75th moving down a line. SAL KHAN: I see. DR. LAURA BACHRACH: And the year after is on the 50th percentile. Now, at that point in time, the child has theoretically a normal height because it's within the curve. But there's something very abnormal about that rate of growing. And that's the child that's more worrisome than the shorter child. SAL KHAN: Fascinating. DR. LAURA BACHRACH: So bottom line, when a child would come in to present to me because of a concern about growing, I'd first of all try to decide if they're are short and if they're growing normally. And those are two different questions. The first question is, are they short? And are they short can be defined by looking at these curves. These are curves representing the spectrum of normal height for a healthy American youth. And they go from the 5th to the 95th percentile. So you can compare a child to the population as a whole. But I also like to calculate what we call the mid-parental height. OK, this is where we take into account the heights of the parents, because that's the most important determinant. So how we calculate that is as follows. We take the height of mom and dad and average them. SAL KHAN: OK, let's do that. So I'm 5' 9", if I'm wearing decent shoes. DR. LAURA BACHRACH: OK. SAL KHAN: So set that to 69 inches. DR. LAURA BACHRACH: OK. And how tall is the mother of your children? SAL KHAN: She's 5' 6". DR. LAURA BACHRACH: She's 5' 6". SAL KHAN: Which is why I don't let her wear too large heels. DR. LAURA BACHRACH: OK. And are we trying to calculate your son or your daughter? SAL KHAN: Let's do my son, since he's a little older. So let's see, it's plus 66 inches. DR. LAURA BACHRACH: OK. So we'll take the midpoint of that. SAL KHAN: OK, so that's really an inch and 1/2. So it's what, 67 and 1/2 inches between me and my wife. DR. LAURA BACHRACH: Right. And we're going to add 2 and 1/2 inches. SAL KHAN: OK. So that gets us what, to exactly 70 inches. DR. LAURA BACHRACH: Right. And that's the height prediction for your son. SAL KHAN: Oh, very good. DR. LAURA BACHRACH: Plus or minus-- SAL KHAN: Oh, plus or minus. DR. LAURA BACHRACH: 4 inches. SAL KHAN: Plus or minus 4 inches, oh, that's a big difference. DR. LAURA BACHRACH: It's a big difference. But that's the nature of human variability. SAL KHAN: I see. DR. LAURA BACHRACH: OK. Now, if this were your daughter, we would take the 67 and 1/2 inches and subtract 2 and 1/2 inches. Let's do that. SAL KHAN: OK, so that gets us 65, so 5' 5" DR. LAURA BACHRACH: Exactly, plus or minus 4 inches. SAL KHAN: Plus or minus 4 inches. DR. LAURA BACHRACH: So that's something we do. We then calculate-- in fact, let's plot that, right on the curve. This is the boys' curve, so let's plot the 70 inches. SAL KHAN: 70 inches is right over here, OK. DR. LAURA BACHRACH: And then the range of 74. SAL KHAN: 74 to 66. DR. LAURA BACHRACH: Right, exactly-- pretty broad range. SAL KHAN: Yes. DR. LAURA BACHRACH: OK. But if we had a child who was growing well below the curve and we thought the midpoint should be about the 50th percentile, that child would be short for the family. So we always like to take the family heights into account. So number one question, is the child's short? It will depend on what the height prediction is. SAL KHAN: I see. So if my son was tracking down here at the 5%. DR. LAURA BACHRACH: That would be concerning. SAL KHAN: Even if he's growing the two inches every year and he's tracking that, it still would be concerning. DR. LAURA BACHRACH: Well, it would raise some questions in our minds. But that's the more important factor is not just where they on the curve at the moment. But are they growing at the normal rate? And the child who is not growing at the normal rate raises more red flags than the child who's trotting up the curve. SAL KHAN: Fascinating. That's interesting, wow. DR. LAURA BACHRACH: So that's the issue. And that's what we approach every day. We want to look into the various causes, potentially, for growth slowdown. We want to address treatment to the specific etiology. SAL KHAN: And etiology means-- DR. LAURA BACHRACH: Well, for example, if the child has a deficiency of thyroid hormone, we want to give thyroid hormone back. SAL KHAN: So etiology is like the cause. DR. LAURA BACHRACH: The cause. If the child isn't growing because he has a nutritional problem, like Celiac Disease, we want to put him on a special diet to address that issue. Some parents think, well, what we want to do-- my child is healthy and normal and growing normally, but I want to give him some growth hormone. That becomes a topic in itself. SAL KHAN: Right, very good. Well, thank you for this. This was super informative.