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Second Trimester: Images of Your Developing Baby

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. These images reveal all the intricate details of your baby's growth -- from a collection of cells to a full-term newborn. While most women may only receive one or two ultrasounds during pregnancy, which is normal, this slideshow of the 2nd trimester of pregnancy gives you a look at each week of development.
Week 18 Week 18: It's a boy! (16 weeks from conception)

Fetal Size: Length, 5 to 5 1/2 inches, crown to rump; weight, 5 1/4 ounces.

Fetal Development Milestones: Male genitalia continue to form.

What You're Seeing: It's a boy! In this image, it's almost as if the baby is sitting down, legs apart, so that his gender is clearly visible. The sonographer can't always determine a baby's sex during an ultrasound exam (and, of course, the exam is centered on the health of the fetus, not his gender). But here, you can see the baby's penis in the center of the picture.