Pregnancy from week 1 to week 40: everything that happens from conception to birth

The approximate duration of pregnancy is 280 days of gestation, or what is the same 38 weeks from the moment of fertilization of the ovum and 40 weeks from the date of the last menstruation (LMP).

Next, we will take a fascinating journey through the gestation of the human being week by week, from the moment of conception to the day of birth. You will be able to know how your baby grows and the changes that happen in the mother’s body throughout the pregnancy.

Week 1 of pregnancy

In week 1 of pregnancy, you are not actually pregnant yet, since during that week you will have your period.

Vaginal bleeding occurs caused by the desquamation of the functional layer of the endometrium that has been prepared to house the fertilized egg. As there is no fertilized ovum, menstruation occurs.

It is the pre-ovulatory stage, variable from one woman to another, which begins with the first day of the period.

Week 2 of pregnancy

In week 2 of pregnancy, your body prepares for ovulation that will occur, depending on each woman, this week or the next. The egg will be released and fertilized by a sperm, giving rise to a new life.

The fertile days are the days when you have the highest chance of getting pregnant. The cycles of the woman usually span 28 or 30 days, so the central days of the cycle will be the most conducive to becoming pregnant: 14 or 15 days after the first day of menstruation.

Week 3 of pregnancy

In week 3 of pregnancy, the magic moment of fertilization occurs. It’s really when you get pregnant.

The first sperm that reaches the ovum penetrates the external barrier until it enters its nucleus and achieves fertilization that gives rise to a new being.

At the moment in which both gametes fuse, each contributing its 23 chromosomes, a unique genetic combination is given that determines the baby’s DNA, and of course, its sex.

Week 4 of pregnancy

In week 4 of pregnancy, four to seven days after fertilization, implantation of the embryo occurs in the walls of the maternal uterus, where it will continue to develop until the day of birth.

On some occasions, when the embryo implants in the uterus, the endometrial tissue erodes, producing slight bleeding that, coinciding with the time when the period should come down, can be confused with menstruation. This bleeding is known as implantation bleeding.

Week 5 of pregnancy

If you have not yet felt the first symptoms of pregnancy, it is likely that you will begin to notice them now in week 5 of pregnancy, along with the absence of the period. Swelling and tenderness of the breasts, nausea, desire to urinate frequently, tiredness and drowsiness… these are some of the signs that you are pregnant.

Menstruation has not arrived, a week late (in regular cycles) it is time to perform the pregnancy test if you have not done it before.

In this week the embryo is barely three weeks old (corresponding to week 5 of pregnancy) and measures about one millimeter wide and four to five millimeters long. It is beginning to have more differentiated parts in its characteristic “C” shape: the top and the bottom, the left and the right, the front and the back are differentiated.

Week 6 of pregnancy

In week 6 of pregnancy, the embryo’s heart begins to beat regularly, although it is probably not yet detected on ultrasound.

It makes spontaneous movements, but there are still many weeks to begin to notice them, because at this point we are talking about a small embryo of a few millimeters: it measures about a centimeter in length.

From the fourth week of gestation (week six of pregnancy), the embryo begins to develop the vestiges of the future organs and devices, and at this stage it is very sensitive. The most important change that occurs in this last phase of the first month of gestation is the folding of the embryonic disc.

Two kinds of folds occur simultaneously at the cephalic and caudal ends of the embryo, one along its longitudinal axis and the other along its transverse axis. The embryo increasingly takes the form of a vertebrate.

In its interior cavities and membranes are formed that will give rise to hollow organs such as the lungs. The middle part of the edges is crossed by the umbilical cord, which fixes the embryo to the yolk sac.

Week 7 of pregnancy

At week 7 of pregnancy, the embryo is about a centimeter long and weighs less than a gram. Arm buds, hand plate, and shovel-shaped lower limb become visible. The brain is transformed into five areas and some cranial nerves are visible.

We are in the period of organogenesis, because the body’s organs are being formed from the different layers of the embryo. The exposure of the embryo to teratogens (agents that can induce or increase the possibility of congenital malformations) during these weeks (4 to 8), constitutes the most critical period of its development.

Week 8 of pregnancy

The embryo in week 8 of pregnancy has an age of 6 weeks since fertilization occurred. The length from the crown to the buttocks is around 15-20 millimeters, and the weight is around three grams. And although it is so small, it is already extremely complex.

The external appearance of the embryo has been modified by the formation of the brain, liver, somites, limbs, ears and eyes. At this time we can say that it already has characteristics that give it a human appearance.

Week 9 of pregnancy

The embryo at week 9 of pregnancy continues to develop, change and grow. It is already the size of a grape, about an inch and a half. Still too small for us to notice, but for him, the growth is dizzying. The tail at the end of the back disappears: our son looks more and more like a human being.

The embryo can now move even if it does so involuntarily. The development of its nervous system increases and sometimes, as I told you, the embryo is no longer wanted, but it can be detected that it trembles. Your brain does not control these movements, but they are spasms that indicate that it is forming connections correctly.

Week 10 of pregnancy

In week 10 of pregnancy there is a change in the way the baby is named. When the 10th week of pregnancy ends, we stop using the word embryo to call it a fetus.

Now all your organs have formed and the heart, brain, liver, kidneys and intestines are working. They will grow and develop continuously until birth but it is already possible to recognize them perfectly defined.

Week 11 of pregnancy

t 11 weeks pregnant the baby weighs approximately 8 grams and will weigh between 4 and 6 centimeters.

His fingers are already separated, the membranes that joined them have disappeared. Although his head is still half of his body it is completely normal at the moment. The ears are migrating to their final position and the little one can now open and close his hands.

Week 12 of pregnancy

Ideally, the first ultrasound should be scheduled at week 12 of pregnancy, although an earlier one may have been performed to confirm pregnancy.

Our baby, at week 12 of pregnancy, is already the size of a kiwi. It will measure 6 centimeters and weigh about 14 grams, we could make a cradle for it in the palm of your hand.

She does not stop moving, kicking and shaking her arms and head, already formed perfectly, she even seems as if she is pushing herself when she touches the walls of the uterus with her feet.

Week 13 of pregnancy

In the 13th week of pregnancy, your head is still disproportionate but each time we will see how the relative size is more balanced with respect to the rest of the body.

The baby’s fingers are already perfectly separated, he has flexibility in his knees and elbows and he can even suck his finger perfectly.

The intestines are already in the internal part of the body, inside the abdomen of the fetus and not inside the umbilical cord.

Week 14 of pregnancy

At 14 weeks pregnant, it will weigh about 30 grams and will measure approximately 10 centimeters. It looks like a miniature baby.

His facial features are becoming more and more evident and we could even see how he makes gestures with the muscles of his face, sucks his finger and his little hand.

He drinks amniotic fluid and pees inside his belly, flaps his arms and legs, and appears to be happy in his intrauterine life.

Week 15 of pregnancy

As of this week, the skin, which is practically transparent, begins to be covered with lanugo, a layer of very fine hair that we can see at birth and that, as you may have heard or have commented, is normal and then falls off on its own.

His eyes are getting closer to the position they will finally have and, although they are still closed, he begins to be sensitive to the changes of light that reach him through his belly. The ears are beginning to have some of their characteristic folds.

Week 16 of pregnancy

By week 16 he is already between 10 and 11cm. The legs are already longer than the arms and some joints are beginning to differentiate, such as the knees, ankles, elbows and wrists.

He begins to open the fingers of his hands and also begins to close them in what seems to be the beginning of the grasp reflex. Thanks to him, she begins to hold her feet, the umbilical cord, or her hands, one with the other. The nails also appear on the hands and feet.

Week 17 of pregnancy

In the 17th week of pregnancy, when the baby has been forming for 15 weeks, it measures about 11-13 cm and weighs about 100 grams.

It continues to grow and especially its legs, since the head now grows less. Under your skin, a layer of fatty tissue begins to form, which will later serve to protect you from the cold. Their hearing is more developed and can move abruptly if there are loud sounds outside.

Week 18 of pregnancy

In the 18th week of pregnancy, it measures about 13-15 cm and weighs about 150 grams. His femur is now about 2.7 cm and the circumference of his little head is about 15.4 cm.

The heart is maturing, being divided by the two atria and the two ventricles. The atria are still in communication with each other, passing blood from right to left through the so-called foramen ovale, as a measure to prevent the passage of blood to the lungs. The moment the baby is born, when he has to start using them and starts to breathe, that hole closes.

Week 19 of pregnancy

His head, arms and legs are already a size commensurate with the rest of his body and hair has started to grow on his head. The ears and eyes are almost in their final position.

It is an amazing thing, but if you are expecting a girl, her small ovaries that will be no larger than a button already contain primitive eggs that will give rise to the ovules.

Week 20 of pregnancy

In the 20th week of pregnancy, the baby measures 16 centimeters and about 350 grams.

His lungs begin to practice breathing and his digestive system does the same by swallowing amniotic fluid. Your brain rapidly develops areas for the senses, and already has 30 billion neurons.

Around the 20th week of pregnancy, a high-resolution ultrasound called morphological ultrasound is performed, which is of great importance in prenatal control. The doctor who specializes in performing it thoroughly analyzes the baby’s organs to detect possible malformations, although not with 100% reliability.

Week 21 of pregnancy

It already moves vigorously inside your gut making you notice with kicks, stretches and twists it does inside the uterus, where it still has room to move comfortably.

It moves about 50 times an hour, but the moment you most notice its movements is when you lie down to rest, especially if you have eaten before, the baby is activated. During the day, when you are also in motion, you cannot feel them so much.

Week 22 of pregnancy

In week 22 of pregnancy (20 weeks from conception) your baby measures 27 centimeters and weighs almost 500 grams.

You can see their eyelids, nails and eyebrows, although the latter still have no color, they are white fuzz that can be seen above the eyes.

Looking at him, he pretty much looks like a full-term baby, but he still needs to gain weight. Your body fat represents 1% of your body, but from now on you will gain layers of fat, which will help you regulate your body temperature.

Week 23 of pregnancy

You can see that your skin is a thin layer that covers your body, but it is no longer translucent, but begins to look reddish and wrinkled. Layers of fat will gradually deposit under the skin.

His eyes are completing their development, although his color is not yet the color he will be born with as his iris is not pigmented. It will not even be the final color, since it may not be defined until approximately six months and even the first year of life.

Week 24 of pregnancy

Your baby is already about 30 cm in total (about 21-21 cm from head to bottom) and weighs about 600-700 grams. You have an increasing chance of survival in the event of preterm labor as your lungs begin to produce pulmonary surfactant that would allow you to breathe outside of the uterus.

Your baby still has plenty of room in the womb and can move freely and change position often. Although he still sleeps about twenty hours a day, he has frequent short bouts of activity in which he will do more and more articulated cartwheels.

Week 25 of pregnancy

This week the baby is already around 34cm in total, around 22cm from head to bottom, and weighs between 700 and 800 grams. His hair begins to define itself and has a certain color and texture, although these may still change when he is born.

Although his eye color is not fully defined, since he needs light for the pigments to finish forming, your baby already has eyelashes and can open and close his eyes. His hearing continues to develop rapidly and can perceive sounds both from the outside and those that he himself produces when moving in your uterus.

Week 26 of pregnancy

As he still has room in the uterus to float and move, he is quite active and increasingly coordinates his movements. In ultrasounds, you can see him “pedaling” with his legs and press against the uterine wall with his feet. The cuffs are also stronger and can grab the drawstring.

Although it is not very common, the kicks may hurt the ribs, in that case it is best to change position, lying on your side.

Week 27 of pregnancy

The baby is still quite thin, although from now on it will accumulate more fat and gain considerable weight. The length from the crown to the buttocks would be about 24 centimeters (about 36 centimeters in total), and the weight is close to reaching one kilogram.

From this week there is a better chance that the baby will survive if it is born premature. But there are 13 weeks to go to term, so it continues to develop.

Week 28 of pregnancy

The fetus is already about 26 centimeters from the crown to the buttocks (about 36 centimeters in total) and weighs about 1,100 grams. She would already have a chance of survival in the event of premature delivery, although her lungs, which are beginning to function, are not yet ready to breathe air and her body temperature regulation would be poor.

Brain growth during this month is spectacular, the fetus feels more and more stimuli from the inside and those that come attenuated from the outside.

Week 29 of pregnancy

The accumulation of fat continues and the baby is large enough to determine its presentation, that is, its orientation in the uterus (breech or cephalic). However, you will still have time to change this position during the next month.

The adrenal glands of the fetus produce androgenic-type substances that circulate in the blood and, upon reaching the placenta, are converted into estrogen (estriol), to stimulate the production of prolactin in the mother’s body (and prepare the breasts to give breast to baby).

Pregnancy week 30

The bones are already developed, but they are still soft and flexible. To give them firmness, the baby begins to store iron, calcium and phosphorus.

You can already differentiate between sweet and savory flavors. His respiratory system continues to mature, and in fact, your baby rehearses respiratory movements and hiccups every day. But above all, the greatest change is going to be found in the maturation of the baby’s nervous system.

Week 31 of pregnancy

The lungs are practically formed, although they cannot yet breathe outside of the mother. Your skeleton is in full growth and your bones continue to store calcium, phosphorus, and iron.

He can turn his head and “see”, not only distinguish light from dark, and his kidneys are fully functional, eliminating more than half a liter of urine a day.

Week 32 of pregnancy

Your baby’s brain is practically formed, so much so that many doctors see no difference between the brain of a newborn and that of a 32-week-old. His weight is around 1,900 grams and his height is about 42 centimeters and if he were born right now he would have an 85% chance of survival, but his lungs are not yet mature.

Week 33 of pregnancy

This week it is possible that, if he has not already turned around to position himself in the cephalic position, he will do so or start “thinking” about doing it. Now he still can, but in a few weeks his size will make the twist more difficult.

Fetuses of this age have been seen to make rapid eye movements (REM) that are like what we do when we dream. For this reason it is believed that 33-week-old fetuses already dream when they sleep. The question that surely we all ask ourselves is and what do they dream of? Question that has no answer, obviously, because it is impossible to know.

Week 34 of pregnancy

The baby is about 18 inches tall and weighs about 2,200 grams. His lungs are almost fully formed and his bones have hardened but are still very flexible, including those in his head.

His skull is not completely closed yet, which allows him to adapt more easily to the birth canal at birth. For this reason, some babies are born with a cone-shaped or flattened head, but this reverses within a few days of birth.

Week 35 of pregnancy

It already measures about 46 cm from head to toe and the weight is over 2,500 grams. The skin begins to smooth, it begins to deposit fat and the lanugo begins to disappear.

Your kidneys are now fully developed, and your liver is beginning to work as well. Most of your basic physical development is already complete. In the next few weeks, she will focus on gaining weight.

Week 36 of pregnancy

Your baby’s skin is turning pinker due to the accumulation of fat and in most cases he will already be upside down and wedged in. He is also losing the hair that covered him and the vernix caseosa which is a creamy and whitish substance that has covered his skin the entire time it has been inside you. All this will be swallowed and that is what the meconium will form, which will be the baby’s first stools (it is a very sticky black paste).

Week 37 of pregnancy

In the 37th week of pregnancy, it measures about 46-48 cm and weighs about 2,900 grams. His femur is now about 7.2 cm and the circumference of his little head is about 33 cm.

If everything has gone according to plan, by now he will be in a cephalic position, that is, face down, ready to be born. As a baby is already formed, what happens inside the belly is an increase in height and weight to arrive in better conditions, in addition to continuing to receive immune cells from the mother. It is estimated that, in addition, it increases about 15 grams of fat per day, which will help it better regulate the temperature outside.

Week 38 of pregnancy

Your baby is about 50 centimeters tall and weighs about 3,200 kilos. Their little hands can already grasp, in fact they already do so with the umbilical cord that has been their toy inside the uterus.

Its head is covered with hair and it looks like it will be born. Some babies are born with a lot of hair while others are born almost bare, but it is something that can later be reversed. The hair with which it is born tends to fall out throughout the first months of life.

Week 39 of pregnancy

In the 39th week of pregnancy, the length of the baby is about 36 centimeters from the crown to the buttocks (about 52 centimeters in total) and the weight is around 3250-3300 grams.

It continues to receive many nutrients from the mother, through the umbilical cord, which is approximately 1.3 centimeters thick. Antibodies also cross the placental barrier and strengthen the baby’s immune system by the time it is born, and it continues to accumulate fat.

Week 40 of pregnancy

You will finally meet your baby! What will it look like? When the baby is born, it has a purple color, maybe pinkish or yellow. The skin appears covered with vernix caseosa, traces of blood and lanugo… High hormone levels make her genitals appear swollen.

Perhaps the head has anything deformed by passing through the birth canal, but it is normal and gradually the head of the baby will take its final shape.

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