Fetal Development: Week By Week Guide: Month 4

The news of pregnancy brings euphoric excitement, and along with it comes a lot of questions. One of the most important questions being the development of the fetus inside your belly. The fourth month of the pregnancy marks the beginning of the second trimester. We give you the week by week details of the growth of the baby from 13th week to up to 16th week.

Week 13

It is the last week of the first trimester. The fetus has grown to be about 3 inches long and weighs an ounce (approximately 25 grams). The ribs start to appear and the cartilage is being replaced by the bone. The chin and nose are well defined and the child can open and close its mouth. It will learn to suck on its thumb. The movements of the baby can be measured. Although you cannot feel it yet, the baby moves in a jerky fashion; it flexes and kicks. The external genitalia is almost defined. By the end of the 13th week, the baby has its own exquisite set of fingerprints.

Week 14

In the 14th week, the fetus has grown about another half inch and is now around 9 cm long. It now weighs about an ounce and a half (approximately 45 grams). The eyes slowly start to move towards the centre of the face. The nose is more pronounced and well defined and the ears are fully developed. The hair starts to appear on the head and the eyebrows, and the cheekbones are developing. The kidneys start to produce urine. The baby pees into an amniotic fluid around itself. For boys, the prostate gland is developing and for girls, the ovaries move from the abdomen down towards the pelvis. The bones are getting strong and hard day after day.

Week 15

After 15 weeks, the baby grows to be over 4 inches (10 cm) long and weighs around two and a half ounces (75 grams). The baby is able to sense light and can move all limbs and joints. It can move its arms and make a fist. The baby might even be hiccupping inside the womb. It also starts to form taste buds and may savour the mother’s meals. Fingernails and toenails develop but the baby’s skin is still very thin. The bone marrow is continuing to develop in the 15th week; it makes up for the baby’s skeletal system. The muscles and bones also continue to grow. You may begin to feel some movements in the belly as the baby kicks, turns and twists. The baby’s mouth’s roof is completely formed by the end of the week and the ears are nearly in position.

Week 16

The fetus now measures around 5 inches (12 cm) from head to buttocks and weighs around three and a half ounces (100 grams). The baby can hear the external voices. It also starts to sleep and dreams. It also learns to breathe and inhales and exhales small amounts of amniotic fluid. This helps the lungs to grow and develop. The facial muscles’ development leads to expressions such as frowning or squinting. The baby has learnt to grasp with his hands. It kicks and can even do somersaults in the womb.