Secrets of the womb: life's most mind-blowing journey: from single cell to baby in just 266 days. (Life science: human reproduction/cells).

ANGELINE MARIE of Hollywood, Florida, is your typical live-wire 2-year-old, winning smiles, occasional tantrums, and all. But when she was an unborn baby growing in her mother's womb, doctors predicted she'd never be able to do what she now loves--dance to music and crawl up and down stairs. Prenatal (before birth) tests revealed that a small a section of Angeline's spinal cord--a thing bundle of nerve tissue that sprouts from the brain and runs down the center of the bony spine--was underdeveloped. The crippling condition, called spina bifida, plagues 1,500 to 2,000 newborns per year in the U.S. It's not deadly, but it is devastating--often leaving victims with crippled legs and brain damage.

To beat the birth defect, Angeline Marie needed a miracle. And she got one at Vanderbilt University Medical Center in Nashville, Tenn. Doctors there performed a controversial cutting-edge medical procedure called maternal-fetal surgery, an operation on an unborn baby still in its mother's womb or uterus. Surgery didn't cure Angeline Marie--two years later her bladder is weak and her feet slightly deformed--but it did spare her legs permanent paralysis, "Angeline was supposed to be paralyzed, but she's not," says her mom Emily. "And there's supposed to be some brain damage, but she's very smart."

There's no doubt in-the-womb surgery is an awesome feat of modern medicine. But equally amazing: 99 percent of babies sidestep birth defects altogether and are born spanking healthy. Says Vanderbilt's Dr. Noel Tulipan: "It's incredible the natural process of fetal development doesn't go awry more often." But then human development itself--from single cell to tiny human being--is one awe-inspiring trip. Here's how it happens.

THE RACE IS ON

It may be hard enough to believe you once wore diapers and slurped liquefied carrots for dinner. But can you fathom yourself tinier than a grain of sugar? Every human life begins as nothing more than a single round cell called a zygote. It's created when a sperm cell (male sex cell) fertilizes, or fuses with, an egg cell (female sex cell). The union combines hereditary information, or genes, from both the mother and the father, creating a master blueprint for the development of a 10-trillion-cell adult human.

A human never again grows and changes as fast as during the first 56 days of life in the womb--a period known as the embryonic stage. Just one week after fertilization, a zygote balloons to a 100-cell blastocyst. It floats down a 7.5-centimeter (3-inch)-long channel called a Fallopian tube, and lodges into soft tissue lining the mother's womb. Here a network of blood vessels--the placenta--sprouts between uterus and blastocyst, allowing blood from the embryo and mother to meet via the umbilical cord. This life-support tube funnels nutrients and oxygen from the mother to the embryo; it also channels waste products, like the gas carbon dioxide, back to the placenta and into the mother's bloodstream.

Now the embryo starts to grow one millimeter a day. After two weeks of rapid-fire cell division, the clump of cells is poised to become recognizably human. Taking nonstop direction from the genetic blueprint forged at conception, the cells differentiate into three distinct layers. Ultimately, these layers will give rise to every single body organ and part (see diagram, left).

GROWTH SURGE

Nine weeks later, the mother-to-be barely looks pregnant, but inside her womb a 5-cm (2-in.) human fetus (unborn baby from 9th week until birth) yawns, stretches, hiccups, and gulps the watery amniotic fluid it floats in. The clear liquid acts like a car's shock absorbers, protecting the fetus from nasty jolts.

In the next seven months, the fetus shoots up from 25 grams (1 ounce) to about 3 kg (7 pounds). As its brain grows, the fetus begins to sense and explore its home. It even sucks its thumb. "Sucking is a survival skill, and fetuses practice it as early as the fourteenth week," says psychologist Janice DiPietro at Johns Hopkins University.

The sense of taste kicks in: In fact, studies show that fetuses swallow more amniotic fluid when sweetener is added. And a mother's diet can strongly scent the amniotic fluid, which may influence later food preferences, says Julie Mennella at Philadelphia's Monell Chemical Senses Center.

With taste comes the development of hearing. What the fetus hears inside the womb may explain why it responds to its mother's voice shortly after birth. "The womb is about as loud as the average apartment," says DiPietro. The mother's heart pounds, causing her blood to whoosh through her body; and loudest of all is her voice echoing through the amniotic fluid's watery balloon.

By 20 weeks the fetus is 20 cm (8 in.) long--big enough for its first medical exam. Doctors use an ultrasound machine to beam sound waves into the uterus. The waves echo off the baby and a monitor translates the waves into images on screen. Ultrasound images of Angeline Marie revealed her spinal defect. So when she was a 23-week-old fetus, Dr. Tulipan and Dr. Joseph Bruner performed maternal-fetal surgery to fuse the spina bifida lesion (open wound) and protect her spinal nerves during the remaining weeks of gestation (womb development).

HOMESTRETCH 

Despite the noisy womb, a fetus sleeps about 85 to 90 percent of the time. Awake or asleep, it moves on average 50 times an hour! Says DiPietro: "The fetus licks the wall of the uterus. It pulls at the umbilical cord like it's a toy." Deep breathing movements prepare the baby's lungs for life outside the womb. Without enough practice, the lungs won't have strength to breathe on their own. That's why many preemies (prematurely born babies) spend their first weeks attached to oxygen tubes.

But not Angeline Marie. "She was born six weeks early, but her lungs worked perfectly," says her mother, explaining how Angeline has defied the odds from day one. "Angie is very strong-willed. She likes to do things for herself."

RISKY MIRACLE?

Doctors at Vanderbilt University in Nashville, Tenn., perform a successful but controversial operation on a 24-week-old fetus. They gently lift the womb or uterus from the mother's abdomen, then cut into the uterine wall to reach the fetus. Their goal: to treat spina bifida, a crippling spinal defect, by stitching muscle and skin over the unprotected section of the fetus's spinal cord. Opponents say the benefits of the surgery may not prove worth the risk, There is no cure for spina bifida.

Timeline: From Embryo to Fetus

Stages of Human Development

DAY 1 The zygote forms when a male sperm fuses with a female egg. In about 12 hours, the fused cell splits into two identical halves. (Mag: x830)

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DAY 3 This solid eight-cell morula divides to form a hollow ball of cells or blastocyst. It drifts down the Fallopian tube to the uterus. (Mag: x680)

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DAY 24 "From the cell mass a 2 millimeter (0.08 inch) embryo has formed. At this critical stage, if skin cells don't curve over to enclose the growing spinal cord, a lesion in the spine results.

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DAY 14 The embryo's cells separate into three distinct layers.

DAY 26 The popcorn-seed size embryo bends into a C shape; its future stomach appears. The tiny heart is already pumping.

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DAY 90 Rapid organ growth begins during the fetal stage. This fetus floats in a protective watery bubble, the amniotic sac, while its limbs take shape.

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DAY 120 The fetus at 4 months has perfect limbs with fingers and toes. The umbilical cord continues to channel nutrients from mother to child.

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From Three Cell Layers: A Whole Human Being

Just 14 days after fertilization, a hollow mass of cells begins to change, or differentiate, into three distinct cell layers: the ectoderm (outer layer), mesoderm (middle layer), and endoderm (inner layer). Each layer gives rise to cells that will ultimately form every organ and tissue in the body.

ECTODERM: Becomes skin, hair, nails, and nervous system

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MESODERM: Forms muscles, bones, and blood vessels

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ENDODERM: Becomes intestines, liver, gall bladder, pancreas, larynx (voice box), trachea (windpipe), and lungs

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DAY 75 The 3.5 cm (1.3 in.) fetus has ample space to flex its arms and legs in the watery amniotic sac. The temperature in here: 37.5[degrees]C (99.5[degrees)F).

Did You Know?

* During pregnancy the volume of blood in the mother's body can double from an average 5 liters (10.5 pints) in order to provide nourishment for the baby.

* Fetal surgery has been performed successfully since the early 1980s. Now, doctors are performing ground-breaking fetal heart-valve operations.

* About 100 billion neurons, or nerve cells, in a human brain form by a fetus's fifth month in the womb. Many of these neurons last a lifetime.

Cross-Curricular Connection

Nutrition: The vitamin folic acid helps an embryo's cells curve over one another to create the neural tube. Research foods that are good sources of folic acid, and other nutrients vital to fetal health.

Critical Thinking: It will take years of research before scientists know whether maternal-fetal surgery for spina bifida has any long-term benefits. But the operation puts the fetus at risk of infection and premature birth, which can be lethal. Is the operation worth the risk?

IT'S YOUR CHOICE

After reading the article, choose the correct answer(s) to these questions:

1 Which of the following doesn't affect fetal development?

a) gestation

b) placenta

c) fertilization

d) catheterization 

2 A 100-cell embryo is called a

a) morula

b) Fallopian tube

c) blastocyst

d) zygote

3 The umbilical cord acts as a

a) nutrient funnel

b) waste remover

c) shock absorber

d) sound transmiter

ANSWERS

1. d 2. c 3, a and b

CHECK FOR UNDERSTANDING

Name: --

Directions: Fill in the blanks.

1. Every human life begins as a single round -- called a --.

2. The first 56 days of life in the womb is called the -- stage.

3. The -- funnels nutrients from the mother to the cells and expels waste products back to the placenta and into the mother's bloodstream.

4. Developmental period before birth: --

5. For a baby's first medical exam, doctors use -- to beam sound waves into the uterus. The waves echo off the baby and a monitor translates the waves into images on screen.

ANSWERS

1. cell, zygote 2. embryonic 3. umbilical cord 4. gestation 5. ultrasound

Resources

* A Child Is Born by Lennart Nilsson, Dell Publishing, 1990 * "A miracle, and yet," by Maggie Jones, New York Times Magazine, July 15, 2001 * For more images of embryo and fetal stages visit www.visembryo.com/baby/index.html