You're now halfway through your pregnancy, 18 weeks from conception! Once a collection of cells resembling little more than a sphere, your unborn baby now looks much like he will at birth. His body is proportionate with his arms and legs balancing out his head; his features, including his eyes and ears, are in their final position and have begun functioning. Even delicate details, such as his finger nails, toe nails, and the hair on his scalp, are growing. Although your baby appears fully formed, he still has plenty of maturing ahead of him.
For past two weeks, your baby has begun to hear sounds in utero. He can now listen to the sounds of blood rushing around, the air moving in and out of your lungs—and perhaps the most dominant sound, your heart beating. Some mothers even find that after birth the sound of a heart beating, reproduced in CDs, can be soothing to fussy newborns. No wonder, since it's one of the first sounds he hears.
Hearing and other sensory responses are now possible because the connections between the brain and your unborn baby's eyes, ears, and nose are becoming established. As your baby gets ready to be more in control of her own movements, her body is busy making myelin, a fatty substance that coats and insulates the nerves throughout her body so that electrical impulses can travel from her brain out to the tips of her toes and back again. She has as many nerve cells as an adult now.
Although your baby's lungs are still not quite developed enough for him to survive outside your body, you'll hear his heartbeat as a powerful whooshing sound during prenatal visits. It'll sound like a tiny racehorse coming home to the finish line.
By now, you should be feeling your unborn baby move and wiggle. He's adding weight this week and throughout the rest of the pregnancy.
Myelin: Made up of mostly fatty tissue and some protein, myelin is the substance that covers nerve endings and makes the nerve impulses move quickly. Defective or deficient amounts of myelin lead to loss of movement, as characterized with multiple sclerosis.
Images courtesy of the American Institute of Ultrasound in Medicine (AIUM.org).