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Pregnancy is a mystery week by week especially when you get pregnant for the first time. As a future mother, you will sometimes feel confused about your baby’s development. Read on and discover these invisible and yet spectacular changes that take place week by week. Know and understand all that’s happening in your body from conception to childbirth with our detailed week-by-week pregnancy calendar guide.

Table of Contents

  1. First Trimester of Pregnancy
  2. Second Trimester of Pregnancy
  3. Third Trimester of Pregnancy


First Trimester – From Week 1 of Conception to Week 12


The Development of Embryo/Fetus

You have done a pregnancy test at home or in a medical laboratory and it is positive! The adventure will begin and will last for 9 beautiful months.

At this period of pregnancy, the egg takes its place in the uterine cavity, it develops while having more and more intimate exchanges with the maternal organ through the trophoblast. This one will later take the name of a placenta.

Here are the main stages of its development, week by week.

  • Week 1 of Pregnancy

    After fertilization, the egg divides and divides again, until it is 150 thousandths of a millimeter. The fertilized egg begins its cell division between 12 and 20 hours later. The egg also sets off, leaving the fallopian tube where fertilization took place to move towards the uterine cavity. Around the seventh day, the egg becomes implanted in the lining of the uterus. Your future baby measures less than 0.1 millimeters when attached to the uterine wall.

  • Week 2 of Pregnancy

    The embryo is between 7 and 14 days old and is now well implanted in your uterus. The embryo measures 0.2 mm and a tiny amniotic cavity appears containing the amniotic fluids. It consists of 150 cells, themselves divided into three layers called embryonic leaflets. The formation of the respiratory and digestive system starts.

  • Week 3 of Pregnancy

    On the 16th day, the embryo measures about 3 mm. It looks like a small comma with a distinct head and tail settling on the uterine lining. The villi on the surface of the embryo encounter the blood vessels of the uterus to provide nutrients essential for its development. The nervous system, the brain and the spinal cord begin to develop. The heart tube is formed through the fusion of two blood vessels. The heart shapes and starts to beat very slowly now with only 40 beats per minute. The formation of eyes and ears also begins as early as this week of pregnancy.

  • Week 4 of Pregnancy

    Your future baby develops to measure 4 mm and his weight has been multiplied by 10,000! From this 4th week of pregnancy, he looks like a big comma and floats in the amniotic cavity. It is during this 4th week of pregnancy that your first appointment with the gynaecologist takes place. This is to check that the embryo is well nested within the uterus. If he ever found himself in a fallopian tube, we would talk about ectopic pregnancy.

    To calculate your due date and welcome your baby under the best conditions, use a due date calculator and check with your gynaecologist.

    The due date calculator works by entering the date of your last period, the average duration of your cycles and the calculation will start! You will discover the probable due date to know when you are expected to meet your baby.

  • Week 5 of Pregnancy

    The embryo growth continues and now measures between 5 and 7 mm and his face begin to take shape gradually. From the fifth week of pregnancy, the eyes start forming, the nose and mouth are deepened, and the ears are still only small slits.

  • Week 6 of Pregnancy

    The embryo continues his rapid growth. It now measures between 10 and 14 mm and weighs 1.5 gr - still very small and yet in two weeks, his weight has been multiplied by 100,000. Even though this is still unnoticeable, your future baby is now moving in your belly.

  • Week 7 of Pregnancy

    The embryo measures 2.2 cm and weighs 2 g. This 7th week of pregnancy is the beginning of bone tissue formation. His hands are on his stomach and his legs are folded. His fingers and toes are gradually forming.

  • Week 8 of Pregnancy

    The eighth week of pregnancy o8rresponds to the last embryonic phase and the embryo becomes the fetus. The embryo measures 3 cm and weighs 2 to 3 gr. Everything, or almost everything, is already present in these few centimeters.

  • Week 9 of Pregnancy

    The fetus measures about 4 cm and weighs 9g. His face is more and more modelled even if his head is disproportionate (it represents one-third of the whole body). As early as this 9th week of pregnancy, girl or boy, your baby’s sex can be found out. Indeed, his genital and urinary tract are already distinct. But you will have to wait a bit before determining what color will be the walls of the room.

  • Week 10 of Pregnancy

    As of your 10th week of pregnancy, the fetus measures between 5 and 6 cm and weighs about 18 g. His face begins to take on a human form. During your 10th week of pregnancy, it's finally the first ultrasound! A moment rich in emotions where you will become fully aware that a little being is growing inside of you.

  • Week 11 of Pregnancy

    The brain of the fetus continues to develop during this week of pregnancy and approaches more and more the image that one has of the human brain. Finally, vital organs are practically all formed and functioning at this stage of your pregnancy.

  • Week 12 of Pregnancy

    Your future baby starts to move slowly, but you can’t feel it yet! Wait for the 4th or 5th month of pregnancy before living this unique experience. All his internal organs are now working. The nervous system and the muscles are active. The fetus is now 10 cm tall and weighs about 40 g.

Second Trimester – Week 13 to 24 of Pregnancy

The Changes in Mother's Body

During the 2nd trimester, the growth of the fetus accelerates enormously. he moves and his movements are well felt. His senses are awakening. The belly of the mother is growing. By the end of the 2nd trimester, the fetus will measure about 25 cm and weigh around 1 kilogram. Here are the main stages of his development, week by week.

  • Week 13 of Pregnancy

    Your future baby is moving more and more this 13th week of pregnancy. Indeed, now he opens his fingers and even his mouth, he drinks the amniotic fluid and begins to discover the sensation of taste. Indeed, the flavor of the amniotic fluid changes according to your meals. Be careful therefore and choose the right food. The fetus measures 12 cm and weighs 50 g to 65 g.

  • Week 14 of Pregnancy

    In the months that follow your future baby will not stop growing. At this stage of your pregnancy, his skin is very thin, almost transparent; but that does not prevent him from having highly sensitive skin and developing the sense of touch.

  • Week 15 of Pregnancy

    The fetus may still be very small - weighs about 135 grams. His eyelashes and eyebrows are growing at this stage of your pregnancy! Hearing develops and the fetus begins to perceive the sounds around his mom.

  • Week 16 of Pregnancy

    The fetal development rate is the greatest until week 16. The fetus increases during these weeks increase twenty-five-fold in weight.

    The fetus is now 17 cm tall and weighs about 150 grams. His muscles are indeed growing. Your baby moves more and more, and these movements contribute to the increase of his muscle mass and to the good functioning of his articulations. Sleeping remains his main activity, with at least 20 hours of sleep a day.

  • Week 17 of Pregnancy

    The fetus now measures about 19 cm and weighs between 200 and 250 grams. His nails begin to grow, and his blood vessels are now visible through his skin. The digestive system of your future child also continues to develop slowly.

  • Week 18 of Pregnancy

    The fetus’s muscles, nerves and bones are developing, but it is also the development of his senses that is at the heart of this week of pregnancy. He can now completely distinguish bitter, sweet, salty and acidic. Some studies even show that he would prefer sweetness.

  • Week 19 of Pregnancy

    Your future baby continues to develop his sensory, immune and neuronal systems. He also moves better in the amniotic fluid but spends most of his time sleeping.

  • Week 20 of Pregnancy

    The fetus weighs about 400 grams and measures 23 centimetres. His muscles are stronger: he can turn around easily and spins in your belly. His internal sex organs are also evolving thankfully because it is precisely in the coming weeks that you will finally be able to know the sex of your baby. Hearing, touch, taste: his senses also continue to refine.

  • Week 21 of Pregnancy

    The placenta is now in place ensuring at the same time the smooth fetal development. The lungs of your future baby are formed. Having an ultrasound session reveals the sex of the baby as well as notice his rib cage developed. It's the beginning of his breathing movements!

  • Week 22 of Pregnancy

    Your future baby's skin is also developing. Produced in larger quantities, it remains wrinkled because your baby is not yet able to develop fat cells. His skin is covered with vernix caseosa, a substance that protects him in the amniotic fluid. It is also in this 22nd week of pregnancy that white blood cells are being produced by his immune system!

  • Week 23 of Pregnancy

    The fetus moves a lot and does between 20 and 60 movements every half hour. He still sleeps as much, and his brain continues developing: grows at the rate of about 250,000 nerve cells per minute

  • Week 24 of Pregnancy

    He starts developing more control on his muscles and can therefore yawn, put his finger in his mouth, raise his arm, and even catch the umbilical cord! He keeps moving and sometimes bumps on the walls of your uterus. What is important at this time of pregnancy are the movements in response to your external stimulation. When you caress your belly, you cause pressure variations of the amniotic fluid that make him move.

Third Trimester – Week 25 to 40 until Birth


The Development of the Fetus

Your baby is still growing. He is well awake and reacts to noises coming from the outside world. His lungs continue to grow to be ready to take the first breath of air at birth. His eyes are open, and he is sensitive to light sources near your belly.

  • Week 25 of Pregnancy

    From the twenty-fifth week of pregnancy, your baby measures about 30-32 cm, weighs 750 g and his face becomes thinner. His features are more precise as his eyebrows are now well drawn. His fragile little nails have grown, and he finally opens his eyes! but it is very dark in your belly, so he sees nothing. Great novelty he is today able to cry!

  • Week 26 of Pregnancy

    Your baby is 33 centimetres tall and weighs about 900 grams. If your child was born in this 26th week of pregnancy, we would be talking about a very premature baby. He is now able to recognize his parents’ voices so talking to him will help him to recognize you later. He now knows how to communicate with you and does not hesitate to play kicks to answer you when you talk to him. He has now hiccupped more frequently, due to the absorption of amniotic fluid!

  • Week 27 of Pregnancy

    As of this stage of pregnancy, your baby has a well-proportioned head compared to the rest of his body. The connections between his neurons are now installed but his movements are still not coordinated. On the other hand, his respiratory system continues to develop. If your baby comes to life during this week of pregnancy, he will be extremely fragile. He will be considered a very premature baby.

  • Week 28 of Pregnancy

    Your baby measures about 36 centimetres and weighs 1.4 kilos. His brain continues to grow, he regulates his temperature, sucks his thumb, swallows and loves that Dad talks to him! He recognizes the familiar noises of new sounds and reacts more and more with the outside world.

  • Week 29 of Pregnancy

    From week 29 of pregnancy, your baby can taste the amniotic fluid whose flavour changes according to your meals. So be sure to choose the right food for your two. Another change in the baby's life is the appearance of surfactant, a substance secreted by the lungs that are very useful for good breathing.

  • Week 30 of Pregnancy

    You enter your 30th week of pregnancy and your baby is now 37 cm tall and weighs about 1.5 kg. If it's not already done, he takes his final position, head down, to get ready to go out. You will see it clearly in this week's ultrasound. On the other hand, his skin begins to smooth and, week by week, his hair, eyelashes and eyebrows continue to grow. He is now able to swallow and make sucking movements, gestures that will be indispensable once he arrives.

  • Week 31 of Pregnancy

    As early as week 31 of pregnancy, the baby is generally positioned with knees bent, crossed arms and legs, chin resting on the chest. He continues to solidify his little bones. So be sure to choose the right food, especially those high in calcium!

  • Week 32 of Pregnancy

    Your baby's skin has turned pink but is still wrinkled! He perceives the difference between darkness and light but begins to feel a little cramped in your belly! He hears you better, so continue to communicate with him on a regular basis. His bones also continue to form. In contrast, the bones of his skull are not yet strong to facilitate delivery.

  • Week 33 of Pregnancy

    Your baby weighs about 2.1 kilos and he is 42 centimetres. To see more closely what your baby looks like, use the ultrasound at 33 weeks! His brain matures, as does his immune system. His respiratory system is yet to reach maturity, he’s placed in an incubator, in case of premature delivery.

  • Week 34 of Pregnancy

    During the 34th week of pregnancy, your baby does not move much because he is now cramped. Do not worry, even if his movements are not as frequent as before, you will continue to feel his presence. On the other hand, the baby puts his head down, in preparation for childbirth. If this is not the case - do not worry, many babies wait for the 36th week of pregnancy to adapt to this position. Your baby starts practising breathing and swallowing a lot of amniotic fluid. At this stage of pregnancy, you may even feel baby hiccups.

  • Week 35 of Pregnancy

    The baby begins its descent towards the pelvis and positions himself in the delivery canal. Weighing around 2.4 kg, If he is born today, he will no longer be considered premature. All his organs are formed and, from this 35th week of pregnancy, he can now breathe or digest all by himself.

  • Week 36 of Pregnancy

    Your baby will not get fat anymore until you give birth. He should gain only 250 gr per week of pregnancy! If he is born today, he will not be considered premature. As of this 36th week of pregnancy, the baby has protected against many viruses thanks to your antibodies.

  • Week 37 of Pregnancy

    At this stage of pregnancy, he is running out of place and does not move much. However, if you feel that he is not moving at all, head to the maternity ward. Your baby continues to practice breathing. His skull is still not solidified to facilitate delivery. Arms crossed on the chest, head down and legs bent. Ready to go out, he adapts to the position for birth.

  • Week 38 of Pregnancy

    The baby is about 50 cm tall and weighs normally between 3 and 3.3 kg. Your uterus weighs over a kilo and contains about 5 litres of amniotic fluid. You can now lose the mucus plug, which most often marks the imminence of childbirth. He has developed a small layer of fat under the skin that makes it seem a little plumper: they are only reserves to face the first days. He too is impatient to see the world.

  • Week 39 of Pregnancy

    At 39 weeks of pregnancy, your baby weighs between 3.3 - 3.5 kg and he is 50 - 52 cm tall. His organs are ready for birth and his little body is able today to face the outside world. He’s accumulated a blackish substance called meconium, in his intestines consisting of ingestion of amniotic fluid during pregnancy which will be eliminated after birth in the first stool.

  • Week 40 of Pregnancy

    Your baby is nearly here! During childbirth, the contractions will push the baby towards your cervix. It is the pressure triggered by the baby's head that will allow the cervical dilation. His skull’s bones are not completely solid. Your baby will try to make his exit easier by sticking his chin against his body, in order to take up the least possible space.

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