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Growth Curve

The inexact science of raising kids

Laura Sanders

Growth Curve

Growth Curve

Database provides a rare peek at a human embryo’s first weeks

illustration of different systems of a 9.5 week old baby

SNEAK PEEK At 9.5 weeks of pregnancy, a human embryo is almost 16 millimeters long — about the size of a 1-cent euro coin. A new 3-D tool lets users check out (from left) the embryo’s skin, cardiovascular system and skeleton individually, or combined with all the organs.

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When I first found out my daughter existed, she was about half the size of a mini chocolate chip.

I was six weeks pregnant; she was four weeks into development. (The pregnancy timer officially begins two weeks before conception.) Already, the structures that would become her eyes had formed rudimentary orbs and the four tiny chambers of her heart were taking shape. At this stage of development, the embryo’s heart is huge, like a dumpling squeezed inside the torso.

You can see this early human heart and what happens before and after it develops with a new tool, the 3-D Atlas of Human Embryology, published November 25 in Science. The atlas chronicles the very first stages of human development — when growth is literally exponential and an embryo is building bodily systems that will be in place for a lifetime.

Embryologist Bernadette de Bakker and colleagues at the Academic Medical Center in Amsterdam created the atlas to help students, doctors and researchers better understand what goes on in those earliest weeks.

“We might know more about the moon than about our own development,” de Bakker says. Even today, human embryology textbooks often rely on pictures of chick or mouse embryos to describe how humans grow. Any human embryonic data used “is often based on just one or two specimens,” she says.

animation of embryo websiteAnd that’s a problem because, as de Bakker has discovered, not all human embryos are the same.

Her team photographed nearly 15,000 cross sections of human embryos from the Carnegie Collection, a famous set of historical specimens collected from hysterectomies and abnormal pregnancies or miscarriages. De Bakker and colleagues uploaded the photos into a computer program, and then, using digital pencils and drawing pads, traced and labeled every organ and structure in every photo. It took some 75 people roughly 45,000 hours to complete.

What they (and we) have gained is a remarkable look at humans’ first metaphorical steps — the steady developmental march that, eventually, takes an embryo from a bundle of cells to babyhood.

Here are some landmarks in the first 60 days of development (links are to PDFs; save and open in Adobe Reader X or higher for interactive features):

Days 15-17: The embryo and all the membranes that surround it are no bigger than a speck of dust. The embryo itself is a speck within the speck, and consists of just three layers of cells. From these layers, all organs and body structures will form.

Days 19-21: What a difference a few days make. The embryo is now about the size of a pinhead and has laid the early groundwork for the heart, gut, skin, muscles, skeleton and brain.

Days 21-23: A furrow of tissue that gives rise to the brain and spinal cord has now begun to fold together, forming the neural tube. If the furrow doesn’t close properly, the spinal cord could protrude from the backbone, a birth defect called spina bifida.

Days 28-32: The embryo, now at the half mini-chocolate-chip size, starts to take on a textbook look, fledgling head and lower body curled toward each other — a rough draft of the classic fetal position.

Days 35-38: Short paddlelike arms and the first nubs of legs have emerged. The embryo is now almost the size of a ladybug. 

Days 44-48: It’s now a slightly bigger ladybug, and leg bones and hand and finger bones have formed. The liver, suddenly, has ballooned in size, filling much of the lower half of the body cavity.

Days 51-53: Chubby fingers have sprouted from once clublike hands. Toes are not visible yet, but toe bones are in place. The embryo is roughly marble-sized.

Days 56-60: The embryonic brain is a giant bulbous globe now, more than a third of the entire body — which is about the size of a cherry tomato. Skinny arms and legs fold close, and a plate of skull has started to stretch across the back of the head.

Give it another 30 weeks or so and that tiny embryo will grow to the size of a bowling ball. Comparatively, a little chocolate chip doesn’t seem like much. But development-wise, it goes through something pretty huge.

Human Development,, Neuroscience

What not to do when your kid tells a lie

By Laura Sanders 9:00am, November 11, 2016
We teach children that lying is naughty, but it’s actually a sign of good brain development.
Human Development,, Health,, Neuroscience

Screen time guidelines for kids give parents the controls

By Laura Sanders 6:00am, October 23, 2016
New recommendations for children’s media use are more nuanced than earlier guidelines, a change that reflects the shifting technology landscape.
Human Development

Baby-led weaning is safe, if done right

By Laura Sanders 9:00am, October 14, 2016
Babies who fed themselves solid foods, called baby-led weaning, were no more likely to choke than spoon-fed babies, a new study finds.

Don’t cocoon a kid who has a concussion

By Laura Sanders 3:00pm, September 29, 2016
Parents should fight the urge to limit kids’ activities after a concussion.

Maybe you don’t need to burp your baby

By Laura Sanders 9:26am, September 15, 2016
Everybody does it. But burping babies after a meal may not cut down on crying or spit-ups, a study suggests.

Doctors need better ways to figure out fevers in newborns

By Laura Sanders 12:54pm, September 2, 2016
When a very young baby gets a fever, doctors scramble to figure out the cause. A new type of test may ultimately help identify whether the culprit is bacterial or viral.
Health,, Science & Society

Tired parents don’t always follow sleep guidelines for babies

By Laura Sanders 8:00am, August 23, 2016
Night videos revealed parents putting their babies to bed in unsafe environments.
Science & Society,, Health

Keep it simple when choosing a sunscreen for your kid

By Laura Sanders 7:00am, August 14, 2016
For parents swimming in a sea of sunscreen choices, look for a few key attributes.
Health,, Immune Science,, Human Development

Nail-biting and thumb-sucking may not be all bad

By Laura Sanders 3:00pm, July 20, 2016
Nail-biters and thumb-suckers may actually be warding off allergies by introducing germs to their mouths, a new study suggests.
Human Development,, Neuroscience

Moms’ voices get big reactions in kids’ brains

By Laura Sanders 7:00am, June 13, 2016
Mothers’ voices get big responses in kids’ brains, a neural reaction that may lead to feelings of calm.
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