3rd trimester: development of the fetus

Our today topic is development of the fetus in 3rd trimester.We will share the development of the fetus.Development Of The FetusBaby is still growing. He is well awake and reacts to noises and caresses on his stomach. He is preparing to be born. His lungs continue to grow to be ready to take their first breath of air at birth. In the long term, it will weigh from 3 to 4 kilos and will measure nearly 50 cm. Here are the last stages of its development.

For the beginning, see our Fetal Development Fact Sheets during the first and second trimesters.

Week 29: he works hard!
Week 30: he keeps his eyes open
Week 31: warm thanks to its fat reserves
Week 32: he’s rattling a lot!Development Of The Fetus
Week 33: less room to move
Week 34: from red to pink
Week 35: a mature brain
Week 36: He trains to breathe
Week 37: finally ready for a child’s life
Week 38: vigorous movements
Week 39: he is patient while sleeping
Week 40: he will be among you soon!


3rd Trimester: Development Of The Fetus

Calculation of duration of pregnancy
Since it is difficult to know the exact day of fertilization , health professionals calculate the duration of pregnancy in weeks of amenorrhea, that is to say without menstruation. The calculation of the date of birth therefore begins on the first day of the date of the last menstruation. This calculation method adds 14 days to the duration of the pregnancy. With this way of calculating, so you are not pregnant during the first 2 weeks and fertilization takes place in the 3 th week of pregnancy.

Week 29: he works hard!
Early in the 3 th quarter, its digestive system is functional. He continues to drink a lot of amniotic fluid and saves a range of flavors through your diet! In addition, the odorous substances carried by the amniotic fluid give him a first olfactory experience likely to influence his preferences after birth.
At this stage of his development, his bones are fully developed, but they are still soft. His muscles gain volume. His eyes are partially open and the lashes are formed. His skin becomes smoother.Development Of The Fetus

As he makes a lot of effort, his nutritional needs are very important. He needs a good amount of protein, vitamins and minerals (especially calcium and iron) that he draws from your diet.

Inside the uterus , the space available to the fetus is limited. His movements become more restricted, which does not prevent him from continuing to push and stretch. And it shows!

Week 30: he keeps his eyes open
At this stage, the fetus’ eyes are open most of the time. He is even able to see, but his vision remains limited. He can see 20 to 30 cm in front of him. He also perceives noises and voices.
The organs are almost entirely formed with the exception of the kidneys and lungs which require more time. This is his 3 e pair of kidneys! At the embryonic stage, he has already had 2 other pairs of kidneys that have disappeared to make way for this new pair, the one he will have for life.Development Of The Fetus

The structures of the brain are strengthening. The sheath that surrounds the nerve fibers (myelin) continues to grow and this will continue intensely during the first years of life. You will note it among others by the development of skills such as walking, language and training in cleanliness.

The bone marrow has taken over the liver and spleen for the production of red blood cells.

His growth slows down a bit, but he continues to gain weight.

Twenty-eight weeks after fertilization, the fetus measures about 27 cm from the head to the coccyx and weighs nearly 1.3 kilograms. He begins to feel a little cramped in the womb.

Week 31: warm thanks to its fat reserves
Another step towards the autonomy of your future baby: the central nervous system is now able to control the temperature of his body, thanks to the reserves of body fat. Moreover, the appearance of the fetus has changed: it is rounder!Development Of The Fetus
Inside his lungs, blood vessels have developed. The respiratory movements are more and more regular.

The testicles are now descended into the scrotum. The oocytes – which will become the eggs – have completed their development. They will “sleep” until puberty, at the beginning of menstruation.

Some fetuses already have their heads down. Often, they keep this position until delivery.

The hair and nails continue to grow: you may be surprised at their length at birth.

Week 32: he’s rattling a lot!
You feel it stir and make great movements of the arms or legs. From time to time, a wave deforms your whole belly: here it is that changes position. Soon he will be too cramped to do the same.
At the end of pregnancy, the weight gain of the fetus is at great speed V. It takes half of its weight at birth during the last 7 weeks of pregnancy.Development Of The Fetus

His heart beats at 130 to 140 beats per minute.

It measures 28 cm from the head to the coccyx and weighs 1.7 kilos.

Week 33: less room to move
The fetus has much less room to move. He is curled up: legs folded, arms crossed and chin on the knees. His body has the proportions of the newborn (head, body, limbs), but it will take advantage of the next weeks to grow a little more and, especially, to gain weight.
He is still fidgeting a bit even if he moves much less compared to previous weeks. This decrease in fetal activity is normal at this stage.Development Of The Fetus

If you have not done so already, the fetus will tip upside down for delivery. His head will rest on the bones of your pelvis where it will descend gradually. By the time of delivery, it will be ensured during your medical visits that the fetus does not turn upside down again.

If it were born today, the baby would have a medium prematurity (this is the most common). His chances of survival would be very good.

Week 34: from red to pink
During the last weeks of pregnancy, the fetus swallows a lot of amniotic fluid and pours a good amount of urine (about 2 tablespoons each hour) into the amniotic pouch. The placenta works at full speed to drain and eliminate waste, and your kidneys too! Remember to drink enough water. A simple trick, drink to satisfy your thirst and make sure the color of your urine is not too dark. If you are well hydrated, your urine will be pale yellow.Development Of The Fetus
In its intestines, meconium accumulates. It will be eliminated in the first time after the birth. These are the first stools.

At this point, the majority of organs and systems are now fully functional. Some nonetheless benefit from the last weeks to complete their maturation. This is the case of lungs, bones, skin, nails and hair.

The bones continue to grow and thicken. The bones of the skull, however, remain malleable for delivery. They are not welded together. Fontanelles (spaces between bones) will not close until several months after birth

The placenta brings a lot of calcium to the baby. The baby’s calcium level is now higher than that of the mother.

The skin of the fetus has taken a pinkish hue (instead of red). The nails now cover the entire fingertips. Those toes, however, take a little longer to grow.

This week, the fetus is about 30 cm from the head to the coccyx.

Week 35: a mature brain
This week marks the beginning of your last month of pregnancy. Two important structures have reached maturity. The brain has completed its fetal development. But it will continue to change throughout life. He keeps a plasticity that allows him to make new learning at any age.Development Of The Fetus
The same goes for the immune system of your future baby. During pregnancy, he has integrated your antibodies to forge a first immunity. He too will continue to develop after birth.

The last weeks of gestation are good for the fetus. His digestive system and lungs are almost mature. In addition, he continues to develop his fat reserves for his birth. It will take about 230 g per week in the next month. Now his little limbs are becoming round. Baby takes his time to look good!

He is more and more cramped. Around him, there is only about a liter of amniotic fluid left.

Week 36: He trains to breathe
Inspire, expire … Your future baby is training! Hic! Hic! He still has hiccups. It’s normal. He practices breathing and develops his lungs. But right now, he is breathing amniotic fluid. He swallows at the same time and it gives him hiccups. Of all the organs of the body, it is the development of the lungs which is the longest.Development Of The Fetus
Otherwise, he continues to gain weight. He now has beautiful round cheeks!

In preparation for delivery, he gradually loses what was his protection in the uterus: lanugo (down) and vernix caseosa (viscous substance).

Week 37: finally ready for a child’s life
Your future baby is now considered full term. It can happen at any time. All his organs are functional. He has enough strength in himself to survive and start his life as a child.Development Of The Fetus
But it is the fetus who will decide, in a way, the moment of his birth. When it is too cramped, it will secrete a hormone that will cause contractions. In the meantime, you may feel his head getting deeper into the pelvic area (this transition is called lightening). And from time to time, through the tight skin of your belly, a small elbow or heel spring … We can even recognize them!

Week 38: vigorous movements
Baby is all beautiful! The layer of vernix (the viscous substance that protects the skin from the amniotic fluid) has now detached and floats in the amniotic fluid that is milky in color.Development Of The Fetus
The heart is complete, but will be slightly modified after birth, because some openings between the cavities of the heart are no longer necessary. He beats harder and his heart rate slows down.

His movements are vigorous and the grip reflex is well developed.

Your baby could now weigh about 2.9 pounds.

Week 39: he is patient while sleeping
Your baby sleeps a lot, he is waiting. He has no room to move. His limbs are folded and close to the body, his chin rests on his knees.Development Of The Fetus
Its growth is now slow, but it continues to grow.

Week 40: he will be among you soon!
All organs are now formed, except the lungs that will finish their development at birth: they will need a few hours to really find the rhythm of breathing. Now, your future baby has all the necessary reflexes to start his development in the outside world. The lanugo falls entirely during this week.Development Of The Fetus
His weight should not really change from birth. Boys tend to be a little bigger than girls at birth, but remember that these are only averages. Many variations are possible and normal.
It takes a little longer than the planned date? This is a very common situation, especially during a first pregnancy (only 5% of deliveries occur on time). The doctor will discuss with you whether to consider starting the delivery. Certainly, he will be here soon!


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