At the 14-week mark, your baby’s ear will begin to appear with its signature folds and helical pattern (although he/she still won’t be able to hear!). The chin will begin to separate from the neck as the jaw and neck lengthen. The baby’s thumb will be more distinctive than the rest of its fingers.
At the 16-week mark, the baby’s ears will be functional and they will begin to recognize your voice! For the first time, your baby’s head will be smaller than its body. The lungs continue to develop and branch out. The lips and mouth will be well formed, yet they will not have developed their sense for taste.
At the 17-week mark, a doctor may be able to first hear your baby’s heartbeat. The baby’s arms will now be proportionate to the rest of the body. Calcium is hardening the baby’s bones and the early tooth buds can be found.
At the 18-week mark, you may finally be able to feel your baby kicking (you may have to wait up to week 22 however). Doctors should also be able to determine the gender of your baby. Fingerprints and toeprints will be developing during this time. The baby’s heartbeat should be easily heard at this point.
At the 19-week mark, your baby will be recognizable as a mini-human, complete with all fingers, toes, and a visible rib cage. A fine protective hair called lanugo envelops the skin. The baby’s joints are still highly flexible (as they are made of cartilage and gradually are hardening with calcium into bone).
At the 20-week mark, your baby will begin to explore its surroundings. A baby’s toes can even reach the mouth! The limbs are still very flexible for the sensitive lips and mouth. You won’t be able to feel any of the baby’ movements that do not hit the side of the uterus.
At the 21-week mark, the nail beds have begun to form and the nails will eventually start to grow. The eyelids will still be fused shut to protect them from your baby’s wandering limbs. The connections in the brain that link senses to their appropriate body part are starting to develop. Fat reserves in the baby’s body will make the baby’s skin appear less translucent. The fat also acts as an energy reservoir for your baby.
At the 22-week mark, stem cells in the bone marrow are rapidly creating red and white blood cells. There isn’t as heavily a reliance on the placenta as before. A baby has the ability to shift around multiple times a day, appearing as a somersault in the womb. The vertebrae have formed to protect the vital spinal cord.
At the 23-week mark, the ears have matured to the point where a baby can begin to respond to many sounds. The nervous and muscular systems have also matured substantially, allowing the baby to begin to learn. For example, if a baby hears the same sound repeated, they will learn to not be startled by it. Your baby will be able to purposefully grasp the fingers shut and suck on his thumb.
At the 24-week mark, the lungs are rapidly improving to ready themselves for use and the heart rate has slowed to show a continuous beat. The baby’s skeleton will have started to harden.