You're already starting your third month, and though you can't feel them yet, your baby is actually starting to make small movements. The baby's nerves and muscles are starting to be in good working order, and she can now bend her arms!
Your baby's rapid growth continues, but the furious rearrangement of cells has nearly stopped. Soon your baby will no longer need the yolk sac that once provided blood cells, because her bone marrow, liver, and spleen are starting to take on that task. In fact, almost all of the organs are beginning to function. Her liver is secreting bile, and her pancreas is producing insulin.
By now your baby's heartbeat is about 160-170 beats per minute. That's about as fast as the human heart rate ever gets! She's slightly over an inch long, and she will more than double in length before the end of this month. The heart is now divided into four chambers, and the valves that will help funnel blood in and out of the heart are forming. Although your baby's heart is beating, your healthcare provider probably won't be able to pick it up during your prenatal office visits quite yet. Give it another week or so.
The umbilical cord is your baby's lifeline in utero—connecting Mother and Baby. Made up of three spiraling vessels (one vein and two arteries), the umbilical cord provides oxygenated blood to help your baby breathe. Connected at your baby's abdomen, one vein carries blood to the baby's heart while two arteries carry blood out of baby's heart and back to the placenta. This system of pumping blood in and out of your growing baby's body not only provides oxygen and nutrients, but also removes any waste that your baby produces as he's developing. Along with your baby, the umbilical cord will continue to mature and strengthen to provide everything your baby needs to survive and mature.
The constant blood flow is helping your baby-to-be's limbs develop and lengthen. He already has the beginning of arms, legs, and fingers; this week his toes are also taking shape. Inside those limbs, bones are forming. As those bones develop, joints such as elbows, ankles, shoulders, and wrists are helping your baby move more freely. You won't be able to feel all this movement because your baby-to-be is still so tiny—even though a sonographer could capture it with an ultrasound.
If you could see your baby, you'd discover that her head is more rounded and more upright on her developing neck. The plates of her skull are forming. Her eyes are still on either side of her head, but they are starting to move forward as her head grows. The tip of her nose has formed, her ears are continuing to form, and she now has tubes leading from her throat to her lungs.
Another fun note: Baby's eyelids are forming this week!
Vein: A vessel that most often carries deoxygenated blood to the heart in a human's circulatory system. The blood is then oxygenated and sent throughout the body through arteries.
Artery: A vessel that most often carries oxygenated blood away from the heart in a human's circulatory system. Differs from veins in that vessel walls are often thicker and more muscular.
Images courtesy of the American Institute of Ultrasound in Medicine (AIUM.org)