Stages of Pregnancy Week by Week

What My Baby Looks Like in Week 4

Discover how your baby is beginning to develop from a blastocyst to an embryo in week four. Plus, you may get a positive result on your pregnancy test this week.

The small collection of cells known as a blastocyst has successfully traveled down your fallopian tube and implanted into the uterus. The implanted cluster of cells is now called an embryo and is smaller than a grain of rice. The implanted embryo has started to produce hormones that may register on a home pregnancy test, yielding a positive result. For some women, the test will not register as positive for another week.
Illustrations Courtesy of the Sprout Pregnancy App

Illustrations Courtesy of the Sprout Pregnancy App

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An Inside Look

Take a unique look at Baby's development inside the womb this week.

Your Growing Belly

A month-by-month photo gallery of pregnancy.

Your Growing Baby

Your baby is the size of a poppy seed.

Your Pregnancy Week 4

Learn more about what's happening with your pregnancy this week including your baby's latest fetal development milestones, your changing body, and tips to help you along the way.

You're Pregnant! Now What?

To-do tasks to get you through the next nine months.

Ask a Question

Got a question? We've got answers from experts and parents who've been there.

29 Ways to Chart Your Pregnancy Needs

Be prepared to share your detailed information with everyone: your medical history with your doctor, your 1 AM pickle cravings with your partner, and your contractions with your prenatal provider. Our A-Z pregnancy downloads make things easy!