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First Trimester: Images of Your Developing Baby

Do you know what to expect in the first trimester of pregnancy? We've partnered with the American Institute of Ultrasound Medicine (AIUM), Johns Hopkins, and the March of Dimes to create this unique peak into Baby's development inside the womb during the first trimester. These images reveal all the intricate details of your baby's growth. While most women normally receive one or two ultrasounds during pregnancy, this slideshow of the first trimester of pregnancy gives you a look at each week of development.
Week 4 Week 4 of Pregnancy

Fetal Size: Not measureable.

Fetal Development Milestones: Positive pregnancy test!

What You're Seeing: The small circle at the center of the sonogram may not look like much, but that little sac is a kind of baby cocoon called a gestational sac. The cells that make up this sac will begin to specialize. Some cells will become part of the placenta. Some will form the amniotic sac that will fill with fluid to cushion your developing baby. Other cells are destined to form everything from delicate eyelashes to muscles and skin. But that's still a long way away.