Foetal development week by week, month by month and growth chart

By the fourth month of pregnancy, the major organs have already formed but the baby continues to grow in size. It grows doubly during this month from 7 centimetres to 14. The eyelids still remain fused and the eyebrows and eyelashes begin to form as the baby grows some hair. This month witnesses three major events, the first being that the appearance of a larger head and a smaller body diminishes as the body of the foetus grows. Second, the foetal heart sound can now be heard with the help of an ultrasound scanner. Excited, aren’t you? Hold on, there is more. Your baby also begins to move starting this month and if you are lucky enough, you may feel some of these. These movements are quite minute and often involve thumb sucking, which may be negligible in terms of a movement but makes for an essential life skill. Not just this, your baby may even get hiccups and develop a faint cry during this month.

In the fifth month of pregnancy, 6 to 8 inches long foetus, weighing about 360 grams, is going through a lot of physical changes. The skin of the foetus gets coated with a thick, creamy layer called vernix, which protects it from the amniotic fluid surrounding it. The muscles and bones continue to develop and it has well-defined arms, hands, nails, fingers, eyelids, eyebrows, eyelashes and has fine hair. The movements of the baby continue to enhance and it can now yawn and stretch, in addition to sucking its thumb. It may also be able to open its eyes at times, which means that the eyelids, which were completely shut till now, begin to be functional.

Another peculiar movement you may feel during the 5th month is the much-awaited baby kick and turns. The baby starts developing other important functions like cognitive skills and an improved immune functioning. It also follows a proper sleep-wake schedule now. However, this may be different from your sleep cycle, which is likely to disturb your sleep. The foetus also begins to develop its unique set of fingerprints during this month.

During the sixth month of pregnancy, the foetus immensely increases in size and moves more often. This may be the first time you feel the foetus moving and may experience around 8 to 10 movements every day. This is a sign that your foetus is healthily developing. It now weighs half a kilogram and is 8 to 10 inches in size, which means that it has a fair chance of survival if it is delivered prematurely during this month but that sure has a high risk of disabilities.

The major features of the baby are well-developed by now and it continues to improve the finer features and grows in size during this month, which finally makes it larger than the size of the placenta. Its skin is covered by a layer of fine hair called lanugo, which helps to keep it warm. The ears of the baby are developed and it can probably hear outside sounds. So, you can carry on with your baby talk from now on.

The bones of the foetus are continuing to develop and also start taking a proper form to ascertain an upright posture post birth.

Your baby is growing really quick now. It already weighs a kilogram and is 10 to 13 inches in size. Explains much of the weight gain? Rapid growth, development and organisation of the foetus occurs during this month. The organs and systems, which were formed initially, continue to refine during this month but your baby is still covered by the vernix. Fingerprints and even footprints form well and the brain continues to grow and differentiate with an increase in its surface area. This initiates the development of osseous growth points in the skull, which is required for bone expansion post birth.

Not just the brain, its lungs also continue to grow and branch profoundly, improving the chances of premature survival to almost 85%. As your baby grows in size, the space inside your womb seems limited. So, adjusting movements are more than the previous months. As the baby rolls, turns, twists and swishes, you may feel at least 3 movements in half an hour, which indicates that it is quite healthy and active. It may also respond to certain sounds and sensations now.

(Read more: Pregnancy month 7 baby movements)

A major development that occurs during the 8th month of pregnancy is the change in foetal position. It moves around and adapts to a cephalic position by fixing its head between the pelvic bones. This aids in a normal delivery and the foetus stays in this position till then. This also prevents it from swimming around in the amniotic fluid.

Talking of amniotic fluid, it can be seen that its levels diminish during this month, which is an indication of the optimal functioning of its kidneys. Neuronal connections continue to improve and in addition to sound, the foetus may also be able to perceive light.

And it obviously also increases in size. It weighs up to 2.1 kilograms by now and 45 cm in length, which is quite close to its delivery size. The thin layer of hair covering the foetus’s body now sheds as it prepares itself to be born and its external genitalia also develops well. Displacement of testicles and development of vulva occurs in male and female foetuses respectively. The baby has a very high chance of survival if delivered now, but, it may require to spend a few days under intensive care.

During the ninth month of pregnancy, the baby is well-developed and is just waiting to be born. If it has been given the right nutrition till now, it will attain a size of about 51 centimetres and can weigh up to 3.3 kilograms. Since the baby enormously grows in size, it has lesser space to move around. So, you may experience lesser kicks and rolls now but this is not at all a matter of concern. The layer of vernix covering its skin thickens as the baby begins to descend to a lower position in your womb. This, and the cephalic head positioning of the baby, will assist the process of delivery, which will occur anytime soon. Although the baby delivered during this month will still be considered as preterm, it holds an excellent chance of survival but would need medical attention for quite some time.

During the first month of pregnancy, your gestation journey begins when the male and female gametes unite to form a zygote. This occurs at the end of the fallopian tube and it is slowly transported down the fallopian tube into the uterus. While it moves, the zygote slowly differentiates to form a blastocyst. The inner layer of this blastocyst will grow to form the foetus and the outer layer will form its protective coverings.

Upon reaching the uterus, the blastocyst strongly embeds within the uterine wall, which is responsible for its nourishment until the placenta is formed. Zygote formed during the first month may be tiny but it contains all the genetic information which is required to form a baby. This is encrypted in the form of a DNA and is inherited equally from both the parents.

The second month marks the beginning of the embryonic stage of the baby, which was yet just a blastocyst. Slowly, the embryo begins to differentiate to be able to form the basic structures. This process of differentiation allows the embryo to form various types of cells including nerve cells, blood cells, and cells of the kidney and the brain. During this month, the embryo grows in size from 2 mm to a whopping 10 mm, which is how you can predict the rate of differentiation.

You may note that at this point your baby is at a high risk of malformation or defects due to maternal habits like smoking, alcohol or certain infections and medications. So, it is very important to take care of these factors.

As the second month advances, the major organs including the brain and the heart begin to develop. Neural tube forms the core for the development of the brain and spinal cord of the baby, which will start this month and continues until the later months of pregnancy. The lungs and gastrointestinal organs start to differentiate and the heartbeat begins to form. Signs of limbs may be seen in the form of tiny buds and eyes may start forming. During this month, the baby starts to curve within your uterus and takes a tadpole-like form with a head and a tail. The growth is often disproportional and is more within the head area giving the look of a large forehead.

(Read more: 2 months pregnant baby size)

As the third month begins, the embryo loses its ‘tail’ with the formation of the tailbone at the end of the spine. The eyes form and move from the side of the head towards the front of the face and even begin to develop some pigment responsible for its colour. However, the eyes are shut. Other facial features, especially the ear begin to develop and refine during this month along with the development of the digestive system and the intestines.

The baby is 2.5 inches at the beginning of this month, grows another inch by its end and weighs 43 gram. As this growth occurs, the baby acquires a more human form and the limbs, which were mere buds, begin to grow, marking the formation of arms and elbows. The embryo even begins to grow nails and it is officially termed as a foetus at the end of 10 weeks. Sexual organs also begin to differentiate and the genitals form. It still has a large head, though, it can form some RBCs and by now has tooth buds, taste buds and a palate.

(Read more: Pregnancy month 3)