This week your fetus weighs 3-5 ounces and is somewhere between 3-5 inches in length. By week 16 the placenta has thickened to around 1 cm in-depth and is now 30 inches wide and has grown large enough to create a barrier for the baby that protects her from infection. In the coming weeks, the fetus will more than double his weight and add inches to his length thanks in part to his straightening backbone, head, and neck. His legs are also growing longer and developing new muscles and will soon straighten out.
While facial expressions are being practiced, his little peepers are also starting to work somewhat as they perceive light and can make side-to-side motions following light sources through his eyelids which will remain fused for a few more weeks. His ears are also developing and because the tiny bones in his ears are hardened, and in place, he can hear some sounds including the sound of your voice. Some studies indicate baby will recognize songs and sounds outside the womb that he heard while in utero, which is pretty cool and a great reason to turn the volume up on fun music that makes you happy.
- American Association of Pregnancy - Pregnancy Week 16
- Mayo Clinic - Fetal Development- Second Trimester