First week of the embryo

4 weeks ago, shortly after your ovulation, the encounter with a spermatozoa made it possible to fertilize your egg and brought him the paternal genetic complement essential for your pregnancy to begin. A cell was formed, then two, four, eight and so on. Discover the evolution of the fetus during your first month of pregnancy.

Second week of the embryo

The egg thus formed continued to advance in one of your tubes, and after 4 or 5 days it arrived in the uterus. It measures at this time 1 mm. It will then cling to the uterine lining and sink gradually into it in order to comfortably lodge there: it is the stage of the nidation, which corresponds to the end of the first week of pregnancy, and of your third Week without rules.

Third week of the embryo

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Fourth week of the embryo

Evolution of the embryo - Week 1

During the second week of pregnancy, the egg continues to grow and the cells that constitute it begin to organize. The embryonic cells separate into two different layers: the so-called didermic embryo stage (2 layers of cells). One of these layers, attached to the wall of the uterus, will become the baby, the other will give the placenta whose function will be to make the connection with you and to bring to the baby the elements that it needs to grow. At the end of the second week, the egg measures 1.5 mm, and 4 weeks have passed since your last period.

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Evolution of the embryo - Week 2

During the third week of pregnancy, the embryonic cells continue their organization, and a third layer of specific cells appears. The embryo is then called tridermal (three layers of cells).

It is from these three layers of embryonic cells that all the organs of the future baby will be made.

At this point, a difference appears between what will be the top and bottom of the baby: the head-buttock axis appears. The baby's first blood cells are also formed at this time.

The embryo has a roughly elongated shape and is about 1 mm long. The whole egg measures 10 mm and it becomes visible in the uterus by ultrasound (for a better vision of the egg, your gynecologist can be led to perform a vaginal ultrasound). It has been 5 weeks that you have not had your period, and so it is usually at this time that you realized that you are pregnant. A urine pregnancy test, available in the pharmacy, allows you to confirm that your delay of rules corresponds to a pregnancy.

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Evolution of the embryo - Week 3

During the fourth week of pregnancy, the trend is accelerating considerably.

Most organs are placed in place, the buds of the limbs are manifested and a sketch of the nervous system appears, from which the brain, the spinal cord and the nerves will develop. The nose begins to form and the heart to beat ... The embryo now has a specific shape, with differentiated zones: a right side, a left side, a belly, a back. It is then clearly distinct from the other cells derived from the egg, which will give the annexes: membranes of the pouch of the waters and placenta. The embryo bathes and lives now in a pocket containing amniotic fluid.

At the end of the fourth week, the embryo measures 4 mm. It is visible on ultrasound.

Six weeks have passed since the beginning of your last menstrual period, and it is the end of your first month of pregnancy.

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Evolution of the embryo - Week 4

My pregnancy calendar

Every week, your personalized pregnancy tracking: see an example

The first layer will cause the skin, nails, teeth and hair, nose, lips, breasts, and the entire nervous system. The second layer will give, among other things, the muscles and Bones, heart, blood, reproductive organs, etc. The third layer will include tongue, urethra and bladder, lungs, liver and digestive system. >