Week 13 Ultrasound: What It Would Look Like

Your baby-to-be is almost done with the first trimester! In the first trimester, he went from a collection of cells to a fully formed individual in a matter of a few weeks. In the coming weeks, his basic body structure will add tissue—and every part of his body will become more defined. He'll also become stronger. Sometimes this trimester you might also be able to feel your baby kick and wiggle!

Probably one of the most important happenings this week is that your baby-to-be has a functioning kidney and urinary tract system. In other words, he's starting to pee in utero. This is normal and helps his body systems begin to process what he ingests.

Your baby's body skeleton is also adding layers to the rudimentary beginnings of bone. Tissue in his arms, legs, and face will be added to in the coming days. In fact, your baby's arms and legs are more proportionate to the size of the rest of his body.

Another change you can begin to see in the sonogram image is the relation of your baby's head size to the rest of his body. Up until now, his head overshadowed the rest of his body by half. Now, as his body has elongated, his head is only 1/3 the size of his growing frame.

More delicate changes are starting to take place, too. On his fingertips, tiny fingerprints are taking shape. He's often putting these fingers in and out of his mouth. He might even run his fingers over his developing tooth buds. While your baby-to-be may not be grinning any time soon, his earliest smile is beginning to come together.

Terms to Know

Tooth bud: Also called a tooth germ, these are the collections of cells that come together in utero and eventually form a baby-to-be's teeth.

Images courtesy of the American Institute of Ultrasound in Medicine (AIUM.org).