14, 15, 16

month 4
week 14: You are now fully into the beginning of the second trimester of your pregnancy. Essentially, for the next 3 months, your baby will grow and grow. It's full system is in place and just needs to expand. The organs are mature by now.
Your baby's heart beats at twice the rate of yours.
The arms continue to develop. The bending of fingers and the clenching of the fists is now possible. Our baby is a whopping 3 1/2 inches long and is 1 to 2 ounces. S/he begins to practice inhaling and exhaling movements. The eyes and ears continue to move and develop, the neck is still getting longer, and the baby's chin no longer rests on his/her chest. The hands are becoming functional, and the baby is beginning to learn to move/use them (probably more reflex than anything). At this point, our little one is receiving all of his/her nourishment from the placenta.
Over the course of this week, a doubling in size takes place!

15 weeks
week 15: If you have an ultrasound now, you may notice your baby sucking his/her thumb. The bones are getting harder each day. The baby's skin is very thin and transparent; you can see blood vessels through the skin. Lanugo, a very fine hair, covers the body and will continue growing on the baby until around the 26th gestational week of pregnancy.
Your baby begins to hear!
The surrounding amniotic liquid helps the external sounds to travel through from you to him/her. It can hear mother's heart, stomach and especially the voice. Some external sounds can also be heard.
On the other hand, the brain is not yet mature enough to interpret this resonant information.
16 weeks
week 16: If you haven't already, you may begin to feel movement as the baby's bones harden. The legs are now longer than the arms, and s/he is moving those arms and legs frequently, especially since there's still lots of room to move within the uterus.
Fingernails and toenails are growing too. In fact, some babies need their nails clipped right after birth!
Your baby now weighs about 2.8 ounces (80 grams) and measures about 4.6 inches (116 millimeters) in length. Although your baby's first muscle movements were involuntary, this week brings the first voluntary muscle movements. Your baby can hold his or her head erect, and the development of facial muscles allows for a variety of expressions such as squinting and frowning.

(copied from several websites. The funniest thing is when they mention size - some are nearly twice the estimate of others!)