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Growth & Development

Weeks 1-5 of Pregnancy

About the Author
by Gerber Baby Experts

4 min read
Pregnancy (For Mom)

1ST TRIMESTER

WEEK 1

Baby—a gleam in your eye

How baby grows

Week one is actually the week of your last period before your egg is fertilized (about two weeks later) and you get pregnant.

How you change

During this week, your body starts preparing for conception and pregnancy.

WEEK 2

Your body’s getting ready for baby

How baby grows

Right between weeks two and three (about day 14 of a 28-day cycle) an egg will be released into your fallopian tube (“ovulation”).

How you change

At this point in your cycle, your uterine lining is developing as a result of hormones your body is secreting to make the uterus receptive to the fertilized egg.

WEEK 3

Congratulations, it’s a zygote!

How baby grows

During the third week, your fertilized egg is a zygote (created when the sperm and egg unite), moving along the fallopian tube towards the womb. The egg begins as a single cell, which divides again and again, then enters into the lining of the womb.

How you change

Right between weeks two and three (about day 14 of a 28-day cycle) an egg will be released into your fallopian tube—this is called "ovulation." Once the egg has been released, it is fertilized, you become pregnant, and the fertilized egg begins its journey to the womb.

WEEK 4

Blasting into development

How baby grows

By week four, your zygote has continued to divide, becoming a group of cells with an outer shell called a blastocyst. The blastocyst enters the uterus, and splits into two parts that will become the placenta and the embryo.

The placenta carries oxygen and nutrients to your baby and carries waste products away from her. The other half of the egg will develop into the embryo, otherwise known as your baby-to-be.

During this week the following also occur:

  • Spinal cord development. A sheet of cells on the back of the embryo folds in the middle to form a tube that will become the baby's spinal cord.
  • Brain section development. One end of the tube enlarges to form the brain's major sections.

How you change

  • Pregnancy symptoms. Hormones from your ovaries may trigger fatigue, tingling, and aching breasts or nausea.
  • Missed period and possible spotting. By the end of this week you may notice that you've missed your period, although some women do experience spotting. Usually spotting is lighter than your normal period. Be sure to talk to your doctor if you have any concerns at all.

WEEK 5

Growing strong

How baby grows

Your tiny embryo’s still only a bit bigger than an apple seed, but your baby’s very busy creating the three cell layers that will later form organs and tissues. Here's how each layer will develop:

  • The top layer. By the end of this week, the neural folds in the top layer of cells begin to fuse into a tube running from the top to the bottom of the embryo. The folic acid in your diet will help this take place. The top part of this tube will eventually form the front part of the brain. A bulge in the center of the embryo will become your baby's heart, which will start to beat this week. The rest of the tube will become your baby's spinal cord and backbone.
  • The middle layer. These cells will produce the circulatory system, bones, most muscles, cartilage, sex organs, and kidneys.
  • The bottom layer. These cells will form the lungs, intestines, and the beginnings of the urinary system.

How you change

  • Missed period. You’ll have missed your period or have experienced slight spotting.
  • Pregnancy symptoms. You might get morning sickness (feel nauseated) or feel fatigue.
  • Unappetizing smells and tastes. Strong smells or tastes may get to you during this time, so it might help to stay away from oily or fried foods and spicy dishes. Even strong-smelling cleaners and disinfectants may bother you right now.

Good to know

Don't worry if you don't experience these symptoms. You may be one of the lucky moms who sail through early pregnancy without feeling nauseated at all!

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