Your Baby's Development During Pregnancy

November 08, 2009

SEARCH drSpock

my account | sign in

HOT TOPICS

		Pregnancy Symptoms
		Read with Your Kids -- It's Fun!
		Take Our Quizzes
		Play with Your Baby

TOPICS


	Parents are talking about their children. Join the discussion.

Your Baby's Development During Pregnancy

by Robert Needlman, M.D., F.A.A.P.
reviewed by Marjorie Greenfield, M.D.

It is hard to convey in words the amazing events that transform a fertilized egg into a baby. Even pictures can't do justice to the intricate swelling, folding, rotating, and merging of tissues that constitute fetal development.

There are several key processes to keep in mind:

Cells grow and divide: In the beginning there is just one cell, a fertilized egg. By the time of delivery, the infant is made up of many billions of cells. All of these cells are descendants of that first one.

Cells specialize: As the fertilized egg begins to divide, the cells begin to take on special identities and functions. Some cells start on the path to becoming skin and brain cells, for example; others specialize into muscles, bones, blood, or any of the thousands of other cell types. How the cells "know" how to do this is a subject of scientific study and still a matter of some mystery.

Cells move: Following directions written in the genetic code, and markers laid down by other cells, cells grow into organs that have specific shapes: arms, hands, fingers. In the brain, by far the most complicated organ, the cells move and stretch their cable-like extensions from place to place, following precise pathways to create intricate patterns. If any of these complex steps goes awry, the result is a malformed and malfunctioning brain. Amazingly, this complex "dance" works perfectly most of the time.

Structures develop and dissolve: Not only do the cells combine to create organs (lungs, heart, and so on), but whole structures are built only to dissolve away, sometimes leaving the merest traces behind. So, for example, early on the heart pumps blood into two main arteries until one of them "melts" away leaving the normal complement of one main artery, the aorta. In the neck, structures that look like gills develop only to dissolve again, leaving in their place parts of the ear, palate, jaw, and other structures.

To make all of this even more astonishing, all of this growing, shaping, and sculpting takes place in the first 20 weeks or so following conception. From 24 weeks of pregnancy on, everything gets bigger. But the main transformations are already past.

Practical Matters

When I think of these events, invisible but so infinitely full of meaning, I always remember the teacher who first explained them to me and the rest of my first-year medical school class. A brilliant physician and teacher, she would stop from time to time in the middle of a lecture and exclaim, "Isn't is amazing!" And it truly is.

There is also a very practical side to all of this: Each system of the body is most vulnerable to harmful outside influences at the time that it is forming. Since so many body systems are forming in the first weeks and months of pregnancy, this is the time when the risks are greatest of birth defects caused by exposures to certain medications, drugs, radiation, infections, or nutritional problems.

These risks are the subject of the our article Medications, Infections, and Other Exposures in Pregnancy.


RELATED INFORMATION

			Fetal Development

Created September 22, 2000
Reviewed September 21, 2004

| |
| | |

THIS SITE DOES NOT PROVIDE MEDICAL ADVICE. The information drSpock.com provides is for educational purposes only and is not a substitute for professional medical advice. Always seek the advice of your health care professional if you have a specific health concern. Mention or advertisement of any product, service, or brand does not constitute endorsement, guarantee, or recommendation by The Dr. Spock Company. Please read our full Terms of Service.