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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.
woman touching belly Week 3 of Pregnancy

Fetal Size: Not measurable.

Fetal Development Milestones: Fertilization!

What You're Seeing: This week is when your pregnancy really begins. At some point, the sperm joins with the egg as it makes its way from the ovary through the Fallopian tube and then into the uterus. Fertilization takes place inside the Fallopian tube. Once together, the cells begin to divide rapidly so that next week, a sonographer may be able to capture baby-to-be's beginnings during an ultrasound examination.