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## Miscellaneous

Current time:0:00Total duration:12:36

# Childhood growth

## Video transcript

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.