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Share Week 4 of pregnancy

Lola Rovati @Lolarovati

We continue with our tour of Pregnancy Week by Week to stop at week 4 of pregnancy, or week 2 of pregnancy. As you know, the duration of pregnancy is 40 weeks from the date of the last menstrual period (FUM) and 38 weeks from conception.

In week 4 of pregnancy, four to seven days after fertilization, the implantation of the embryo takes place in the walls of the maternal womb, where it will continue to be developed until the day of its birth.

Implantation of the embryo

After fertilization occurs in the uterine tube, the blastocyst, a set of embryonic cells formed from the junction of the egg and sperm, descends into the uterine cavity. There it produces prolongations that will allow it to adhere to the mucosa and "bury" itself in the endometrium, this is what is known as embryo implantation .

Since the blastocyst is implanted in the endometrium is when you start talking about an embryo .

Fourteen days after fertilization, the embryo is firmly nested in its new home . That's where a new being will grow and develop.

Deployment bleeding

When implantation occurs, the body sends chemical signals to prevent menstruation from occurring.

Sometimes, when the embryo is implanted in the uterus, the endometrial tissue is eroded, producing a slight bleeding that, coinciding with the time when the menstruation should fall, can be confused with menstruation. This bleeding is known as implantation bleeding.

The loss caused by the nesting of the fertilized egg in the wall of the uterus can last from one to three days, is usually milder than bleeding by menstruation and darker. Sometimes it is just a drop of blood and in others it can get confused with a light menstruation.

Week 4 of pregnancy

In the embryo, it is only two weeks old and measures half a millimeter. It still has no human aspect, but you can distinguish the protuberances that will later be the head and body of the baby.

The embryo in this stage is composed of three layers that will give rise to the different tissues and organs of the body. The ectoderm (the outer covering) that will give rise to the formation of the nervous system, the mesoderm, (intermediate cover) that will be responsible for forming most of the internal organs as well as the reproductive organs and the circulatory system, the bones, the muscles and cartilages, and the endoderm (inner cover), which will lead to the respiratory and digestive system.

The neural tube and the spinal cord belonging to the baby's central nervous system begin to form. The placenta is also formed, which will be responsible for transmitting nutrients and oxygen to the baby throughout the pregnancy. Meanwhile, that function is fulfilled by the yolk sac, an embryonic annex, which will disappear in the coming weeks.

The pregnancy test

Surely in this week or in the next few days, when you see that menstrual bleeding does not occur, you will perform the pregnancy test.

To make your result more reliable, you should do it with the first urine in the morning, which is the one with the highest concentration of the pregnancy hormone, chorionic gonadotropin hormone (hCG), and expect to have a delay of at least one day .

Some women begin to feel the first signs of pregnancy, such as dizziness, nausea and generalized fatigue. There are even those who intuitively realize that they are pregnant before confirming it with a test.

It is very important that if you have not done them before, you start taking a daily supplement of 400 mg of folic acid. Ideally, start taking it at least a month before becoming pregnant to ensure that the body has a sufficient reserve of this essential vitamin that prevents defects in the fetus.

Pregnancy week to week: from conception to birth

Photos | Bradley Smith in The Multi-Dimensional Human Embryo, BrownGuacamole