The development of the embryo and the fetus: 1st trimester

Our today topic is baby development week by week.We will talk about baby development week by week.The first quarter runs until the 14 th week of pregnancy. The embryo begins to form. His first organs appear. At the end of the first trimester, even if it measures only 9 centimeters, one distinguishes very well its head, its trunk, its arms and its legs. Here are the main baby Baby Development Week By Weekdevelopment week by week

Baby Development Week By Week

Week 1: Why 40 weeks of pregnancy?
Week 2: Ovulation
Week 3: Fertilization
Week 4: implantation of the egg
Week 5: The umbilical cord
Week 6: the neural tube and the first heartbeat
Week 7: the brain
Week 8: he begins to move
Week 9: arms and legs
Week 10: joints and ears
Week 11: the embryo gives way to the fetus
Week 12: his nails start to grow
Week 13: spine and spinal cord
Week 14: he begins to suck his thumb

Week 1: Why 40 weeks of pregnancy?

It is difficult to know the exact day of fertilization . To assess the duration of pregnancy, doctors use the number of weeks without menstruation (amenorrhea). 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, you are not pregnant during the first 2 weeks.

Week 2: Ovulation

Ovulation is when one of the ovaries (left or right) expels an egg . In general, women ovulate 14 days before menstruation, but this number can vary between 11 and 18 days depending on the length of the menstrual cycle . The expelled egg descends along the fallopian tube, the site of fertilization. He then continues on his way to the womb .

The life of the egg is from 12 hours to 24 hours. The fertility period lasts approximately 5 days every month: from 4 days before ovulation to 24 hours after this one. As for the spermatozoa, they can live from 3 to 5 days in the body of the woman.

Week 3: Fertilization

A sperm of the father enters the inside of the mother’s egg: they fuse to become an egg composed of a single cell. It is the fertilization and the actual beginning of the pregnancy.
This egg will take several weeks to develop and become a baby. But already, it contains all the genetic baggage of the child to come: its sex, the color of its eyes, its size, the pigmentation of its skin, etc. All this, in a small sphere that is the size of a pinhead!Baby Development Week By Week

During its first days of life, the egg descends quietly from the fallopian tube to the uterus. During this trip, the egg, single cell, will divide to give 2 cells. These will divide in their turn to give 2 others. These 4 cells will do the same to give 8, and so on. This process is called cell division. Thus, little by little, all the organs, limbs and systems that make up a human being will be formed.
In rare cases, the egg will implant outside the uterus, mostly in a fallopian tube. This is called an ectopic or ectopic pregnancy. The pregnancy must be terminated to protect the mother’s health.

The twins
The “identical twins” come from the same fertilized egg that separated completely into 2 embryos. They share the same genetic code. Their physical resemblance is striking. It will necessarily be children of the same sex. As for the fraternal twins, they are explained by the fertilization of 2 eggs. Their sex can be different.
Week 4: implantation of the egg

The fertilized egg attaches to the mucosa. This step is called nesting. It lasts a few days and requires the production of a special hormone produced by the egg: the gonadotropic chorionic hormone (HCG hormone). She is the one that pregnancy tests detect. The HCG rate doubles every 2-3 days in early pregnancy, peaking between the 8 th and 10 th week.Baby Development Week By Week
The presence of this hormone ensures a significant production of progesterone . Its role: to keep the thickened mucosa in place. The egg nestles there, more and more deeply. It is enmeshed there to feed (in nutriments and oxygen) thanks to the numerous blood vessels which are there.

What does the egg look like at this stage? Its size is about 1.5 millimeters. It contains several cells and has the bumpy appearance of a raspberry. It consists of two layers: an inner part that will form the embryo and an outer part that will become the placenta , the envelope used to protect and nourish the embryo. But already, the first stage of the nervous system is in place. The heart started to beat even though its development is not over.

Baby Development Week By Week

Week 5: The umbilical cord

During this week, the embryo unfolds: it goes from a round to an elongated form. It looks like little hippocampus. Helped by the blood circulation that is taking place, the embryo grows a lot during this week. It is now visible to the naked eye. The heart began its first stage of development. Gradually, the face is drawn: the eyes, the nose, the mouth, the ears.Baby Development Week By Week
The cells specialize. They are organized in 3 groups. Each will constitute different parts of the baby’s body: the skin, the eyes, the ears and the nervous system (ectoderm), the muscles, the skeleton and the blood vessels (mesoderm), the digestive tract, the pancreas and the lungs (endoderm) ).

The umbilical cord now connects the embryo to the mother. Thanks to him, the embryo will receive nutrients from his mother’s diet and oxygen. The cord also allows to evacuate part of its waste. Nestled in the uterine cavity, the embryo bathes in the amniotic fluid .

Week 6: the neural tube and the first heartbeat

During this week, 4 weeks since the time of fertilization, a significant part of the embryo will be completed: the neural tube . It is important because the entire nervous system develops from this structure: the brain, at one end of the tube, as well as the spinal cord and nerves. The ends of the tube will close at the end of this week. Taking folic acid supplements before and during pregnancy serves, among other things, to prevent malformations during neural tube formation, such as spina bifida .
The heart of the embryo beats! During an ultrasound, it is possible that we can see the beats. But this little heart is still in formation: it looks like a little bump. We see it, very prominent, in front of the body of the embryo.Baby Development Week By Week

The embryo resembles a bean from which emerge small buds that eventually form the arms and legs. The neck is also looming. The lens of the eyes and the inner ear begin to develop as do certain organs: the lungs, the stomach, the liver and the pancreas.

Week 7: the brain

This week, brain development will take precedence over everything else! A first draft of the cortex is emerging with the development of both hemispheres, cerebral cortex and gray matter.
The head is formed little by little. The back of the brain becomes wider, causing the embryo to tilt the head forward.

On his face, we can now see the nostrils. The furrow of the gums, where the baby teeth will grow, is already formed. On each side of the head, we can see 2 dark areas: these are the eyes! It is the retinal pigment that gives them that color.Baby Development Week By Week

Vital organs are all developing. However, they are not yet functional. Inside the heart, we now distinguish the 4 cavities.

Week 8: he begins to move

It is the turn of the eyelids and the outer ears (they look like small dimples) to begin their development. However, the first senses to “wake up” in the embryo will be smell and taste. At this stage, the nose and upper lip are already formed. Starting this week, olfactory receptors will appear.
At the end of the limbs, we see small buds. They will form fingers and toes. We also distinguish the location of the elbows and knees. The embryo is no longer static: it moves the trunk and limbs. It moves inside the uterus, but we do not feel it.Baby Development Week By Week

Several vital organs take shape: the stomach, intestine, pancreas and kidneys appear. However, they are not yet functional.

At the end of this week, the embryo measures from 11 to 14 mm.

Baby Development Week By Week

Week 9: arms and legs

During this week, the arms and legs get longer and the joints (elbows and knees) are more precise. We also see the wrists and ankles to draw. Inside, muscles and nerves take shape.
The head always has a large size compared to the rest of the body. But, it gradually rounds off and the neck recovers. There are two dark areas to the eyes (they are for the moment distant on the sides of the head), 2 dimples for the ears and a single opening for the nose and mouth.

On the sensory level, we now find receptors of touch (tactile receptors) around the mouth of the embryo. During this week, the first taste cells will also develop.Baby Development Week By Week

Depending on the sex of the child, the ovaries or testes begin to form. However, it was only during the 3 th month of life genitals appear.

Week 10: joints and ears

The embryo looks more and more like a baby. Its members continued to push: all parts, including the joints, are clearly visible. The toes and fingers are well defined. The embryo can now do a whole range of movements!
The eyelids are now formed and protect the eyes in formation. The (external) ears are now very similar to yours! However, they are still located a little low on the head, near the neck.Baby Development Week By Week

At this stage of pregnancy, the heart rate of the embryo is at least 130 beats per minute, but it can go up to 160 beats per minute. It will decrease slightly and gradually during pregnancy. The heartbeat can be seen using a Doppler, a device that lets you hear the baby’s heartbeat.

Week 11: the embryo gives way to the fetus

An important step has been taken: the embryo has become a fetus ! His head is still bulky compared to the rest of his body. Its growth will now be slower than that of the body and it will continue to grow.
The face is now easy to spot. The eyes migrated from the sides to the front of the face. The eyelids now cover the eyes. The lips are well defined and the fetus can open the mouth. He even drinks amniotic fluid. Fortunately, his kidneys and the urinary system began to function. They filter the swallowed liquid and throw it back into the bladder as urine.Baby Development Week By Week

In the mouth and in the nose, the first cellular structures have been transformed into buds of taste (taste buds) and smell. The same goes for the salivary glands. And this week, the vocal cords will also begin their development.

Week 12: his nails start to grow

All organs and vital systems are now partially formed. The extremities are also polished: the nails begin their development. Until then, part of the small intestine (the intestinal loops) overhanging the umbilical cord. All this is now well inside, inside the belly of the fetus.
In the brain, nerve cells multiply. They connect together creating many synapses. There are already some archaic reflexes. For example: the fetus folds the fingers and toes if something touches the palm of his hand or the sole of his foot. The newborn will keep this reflex for a while, then it will gradually disappear, just like other archaic reflexes. These reflexes testify to the good neurological development of the baby.Baby Development Week By Week

The fetus now measures 6 cm from the head to the coccyx and weighs about 14 g.

The whole uterus is now occupied by the amniotic sac: ideal for your first ultrasound! At the end of this week, the risk of miscarriage drops dramatically. If you have not already done so, you can start announcing the good news around you!

Amniotic fluid
Throughout pregnancy, the baby bathes in a liquid called amniotic fluid. This liquid is vital. It is surrounded by a thin membrane that creates a real closed pocket in the uterus. Thus, the baby enjoys a stable temperature and can move while being protected from shocks and infections. The amniotic fluid also brings him water and some nutrients. But most of the nutrients come from the mother’s blood and come through the umbilical cord. At the time of delivery, the “water pocket” is pierced. It then contains about 1 liter of liquid.

Week 13: spine and bone marrow

The first bone tissues begin to form, including those of the pelvis, ribs, head and limbs. They are rather soft. The spine also develops little by little.
At the same time, the buds of the baby teeth appear. Under the milk teeth will push the adult teeth. These will form later in pregnancy, during the 2 th quarter.Baby Development Week By Week

The blood of the fetus is constituted: the bone marrow produces its first red blood cells.

The thin skin of the fetus is covered with small fine hairs: it is lanugo. It usually disappears before birth. The pigments of the skin (which gives it its color) also develop. The skin, until then, was almost transparent. In addition, tactile receptors now cover the entire face, the palms of the hands and the soles of the feet.

Week 14: he begins to suck his thumb

His face comes alive! Some features are defined as the nose and mouth. The ears have taken their location on the side of the head. The fetus is also able to make certain facial expressions like frowning and grimacing. These are mostly reflex reactions at this stage. Another distinctive element of your future baby appears: fingerprints.Baby Development Week By Week
The fetus starts to react to external stimuli. If you push on your belly, it is possible that the fetus responds by pushing in turn. At this stage, it is also possible that he started to suck his thumb.

The sex of the baby will become apparent this week or the next. In girls, ovarian follicles form; in boys, the prostate becomes visible. At your next ultrasound, you will know the sex of your future baby if you wish.

At the end of this first trimester, the fetus measures 9 cm from the head to the coccyx. It weighs about 40 g.

Baby Development Week By Week

Date Of Delivery

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