The first week of pregnancy is when everything starts, where everything is set up. This particular moment begins with fertilization (encounter between the egg and the spermatozoon) and continues with the migration of the egg into the uterus.
But before seeing in detail, what happens during this first week of pregnancy, here is a first important information concerning the calculation of weeks of pregnancy.
In France, gynecologists count the duration of pregnancy in weeks of amenorrhea (SA = weeks of absence of rules). Thus, the calculation starts on the 1st day of the last period, so about 2 weeks before fertilization (before the actual start of pregnancy). Because it is only in the middle of the woman's cycle, around the date of ovulation, that the egg can be fertilized by a spermatozoon.
And so in reality, the 1st week of pregnancy is the 3rd week of amenorrhea (SA).
A pregnancy has a total of about 39 weeks, about 41 weeks, or 9 months.
This method of calculation has been shown to be effective because it is not possible for all women to safely establish the date of ovulation a posteriori. The first day of the last period, however, is known to all women. So fertilization is very likely about 14 days after this date.
In addition, this more precise calculation method allows the doctor to compare the different values established during examinations regularly performed during pregnancy (for example, height and weight of the fetus) with the mean values. But it often happens that the doctor later corrects the precise date of the beginning of the pregnancy according to the results of the ultrasound examination of the fetus.
With the 1st week of pregnancy also begin the 1st month of pregnancy and the 1st trimester of pregnancy. The trimesters are important benchmarks to differentiate the various phases of the pregnancy, with examinations and very precise steps to carry out.
Useful nutritional advice: If you want to become pregnant, a diet rich in folic acid (also known as "vitamin B 9" or "folate") is recommended. Pregnant women - as well as women who want to become pregnant - should absorb about 0.4 mg of folic acid per day thanks to the diet rich in folate (green vegetables, liver, kidneys.). This vitamin B 9 intake is also recommended during the first weeks of pregnancy.
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Everything begins with fertilization, in the middle of the menstrual cycle, following sexual intercourse during ovulation.
During ejaculation, several tens of millions of sperm are emitted into the vagina. The spermatozoa then pass through the cervix which secretes abundant cervical mucus during ovulation.
A small proportion of them manage to cross the cervix and migrate into the uterus, making their way through the mucus. From there, some progress in the tubes in a few tens of minutes. The others are stored in the uterus where they will survive for several days, then they will migrate to the tubes. A few hundred spermatozoa surround the oocyte (located in the outer third of the trunk); only one of them will enter it. Ovulation occurs in the woman's uterine horn, it is the meeting between a spermatozoon and an ovum released by an ovary of the future mother.
Each spermatozoon, like every oocyte (or ovum), is the only cell in the body with only 23 chromosomes (all other cells in our body have 46). The 23 chromosomes contained in the spermatozoon will fuse with the 23 chromosomes of the oocyte to form the first cell of the baby. This one will thus comprise 46 chromosomes: half brings the genetic characteristics of the mother and the 23 others the genetic characteristics of the father.
This first cell will split to give two cells, then four, sixteen. Thus is formed the egg, which is also called "embryo": a new being, who inherits the genetic traits of his parents is created, and will develop for nine months.
This embryo moves in the trunk through tiny vibratic eyelashes into the uterus, which it reaches in three to four days.
After two or three days of floating in the uterus, it will nest in the endometrium, the lining that covers the inside of the uterus. It is the implantation: the egg will develop extensions that will hang in the uterine lining and become the future placenta that plays the role of "lung" and "digestive tract" to the fetus. The end of the 1st week of pregnancy corresponds to the nesting period.
The future baby then has about ten cells and measures about 0.1 mm.
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Authors: Dorothee Gebele, Dr. Nicolas Evrard