From conception to childbirth, a baby goes through numerous developmental milestones during each month of pregnancy. Pregnant women may find knowing what is taking place with their baby during each month of pregnancy helps them feel closer and helps them bond with the baby and makes their pregnancy more enjoyable.
First Month
Although it may not seem as if there is a lot happening when looking from the outside, a dramatic transformation is underway during the first month of pregnancy. After implanting into the uterine wall and the cells of the fertilized egg begin multiplying quickly. Arms, legs, spinal cord and brain start forming, and the lungs begin to develop. By the end of this month, the baby's heart will begin to beat. At this time, the American Congress of Obstetricians and Gynecologists (ACOG) estimate the baby to be less than 1/2 an inch and usually weighs less than 1 oz.
Second Month
During the second month of pregnancy, bones begin to form and fingers, wrists, ankles and toes begin to form. The inner ear and eyelids also form, although the eyelids will remain closed for some time yet. The genitals also start developing at this time. Amazingly, all the major body systems and organs will have already begun to develop before this month ends. At this time, ACOG estimates that the baby is about 1 inch long but still weighs less than an ounce.
Third Month
All the internal parts of the body will continue to be formed during the third month, but will not be fully developed until later. Muscles and bones begin growing, and the intestines start to form. Although the feet are less developed than the hands, fingers and toes will continue to grow and nails will begin to form. The legs are shorter than the arms at this point, and the backbone is soft and can bend. The buds for teeth also appear. At the end of this month, the ACOG estimates that the baby is around 3.5 inches and weighs a little over an ounce.
Fourth Month
The fourth month is when the outer ear develops and the baby begins to hear for the first time. The baby can also flex his arms and legs at this point, although it is probably too soon for the mother to feel these movements. The external sex organs are completely formed at this point and it may be possible to identify the gender by ultrasound. Eyebrows, eyelashes and fingernails continue to grow. The kidneys function and start making urine. By the end of the fourth month, the ACOG estimates the baby is around 6 or 7 inches long and weighs approximately 5 oz.
Fifth Month
The baby usually becomes much more active during the fifth month and this is the time many mothers are able to feel movement for the first time. The sucking reflux develops this month, and it is possible for the baby to suck her thumb if the hand gets close enough to her mouth. The baby also begins to sleep during this month, and will alternate between being asleep and awake. The gall bladder starts producing bile. At the end of the fifth month, the ACOG estimates baby is 10 inches long and weighs somewhere between 8 oz. and 1 lb.
Sixth Month
During the sixth month, the baby will open his eyes for the first time. The brain is developing quickly, and hair starts growing on the baby's head. Fingerprints and toe prints are also present at this time. Although the lungs are completely formed by now, they will not function until closer to the end of the pregnancy. The baby is approximately 12 inches long and weighs between 1 and 1.5 pounds, according to ACOG.
Seventh Month
The eyes become more sophisticated during the seventh month, and the baby now notices changes in light. The baby regularly kicks and stretches, and these movements are now noticeable to the mother. At this point, the baby can grasp with his hand and may respond to sound. By the end of the seventh month, ACOG estimates the baby is around 14 inches long and weighs 2 to 2.5 lbs.
Eighth Month
In the eighth month, all major development finishes up and the baby begins to put on weight rapidly. The different regions of the brain form, and although most bones begin to harden, the skull remains flexible for childbirth. Taste buds begin to develop at this point, so the baby can tell the difference between sour and sweet. During the end of the eighth month, the baby will be about 18 inches long and weigh about 5 lbs., says ACOG.
Ninth Month
The baby prepares for childbirth during the ninth month. Most babies will turn head-down and may "drop" lower into the mother's pelvis. The skin is less wrinkled this month, and the lungs are now able to fully function without help. The baby puts on a remarkable half pound each week during this last month. By the end of the month, the average baby will be about 20 inches long and weigh somewhere between 6 and 9 lbs., according to ACOG, and will finally be ready to be born.
