Your Baby's Development
By your second trimester, your baby is well developed. This stage of the pregnancy can be very exciting because you may start to feel your baby move at about eighteen to twenty-two weeks. If this is not your first pregnancy, you may even be able to feel movement earlier, at sixteen to eighteen weeks. Your baby looks like a small person now and is continuing to develop every week during this period.
Your Fourth Month (13 to 16 Weeks)
By your fourth month of pregnancy, your baby's fingers and toes are well defined. Eyelids, eyebrows, and nails are formed. Hair is starting to grow on top of the baby's head, and facial features are more prominent. The teeth and bones are becoming harder. The baby is moving her arms and legs and can even suck her thumb, yawn, and stretch. The baby is starting to now respond to outside stimuli. The nervous system is beginning to function, and the reproductive organs and genitalia are now fully developed. At this point your doctor may be able tell through an ultrasound if you are having a boy or a girl. The baby's heartbeat is now undeniably audible through an instrument called a Doppler. By the end of your fourth month, the baby is about six inches long and weighs somewhere around 4 ounces.
Your Fifth Month (17 to 20 Weeks)
During your fifth month of pregnancy, hair on the head, eyebrows, and eyelashes are filling in. A soft, fine hair, called lanugo, covers the baby's body. Meant to protect the baby, lunago is usually shed by the end of the baby's first week of life. Fat is beginning to form on the baby's body to help him stay warm and to aid in metabolism. The lungs, circulatory, and urinary systems are now in working condition. At this point, the retinas in the eyes are sensitive to light. The baby's skin is developing and appears transparent. Your baby can hear sounds such as your voice and heartbeat as well as sounds outside of your body. During this month, you may begin to feel the baby move as his muscles begin to develop. As the baby continues to develop, you will notice more movement. By the end of the fifth month, the baby is about ten inches long and weighs anywhere from 8 ounces to 1 pound.
At this point, you should start sleeping on your left side because circulation is best that way. By the time you get to your fourth or fifth month, lying on your stomach or your back can put extra pressure on your growing uterus and may decrease circulation to the baby.
Your Sixth Month (21 to 25 Weeks)
During your sixth month, the baby is continuing to gain fat to keep its body warm. His or her growth rate is slowing down, but bodily systems such as digestion are continuing to mature. Buds for the permanent teeth are beginning to form, and the baby's muscles are getting stronger. The baby is very active and will respond to sounds and movement. The baby's body is becoming better proportioned. It is beginning to produce white blood cells that will help the baby fight infection and disease. You may begin to tell when the baby has hiccups by the jerking motions you feel. The baby's skin is more opaque than transparent and is wrinkled as the baby grows into it. The heartbeat at this point can be heard more easily through a stethoscope depending on the baby's position. By the end of the sixth month, your baby measures approximately twelve inches in length and somewhere around 2 pounds.