The period of embryogenesis, that is, when the embryo develops and develops, lasts from the first to the 11th to 12th week of pregnancy. After this period, the embryo is already called the fetus. In this case, the first day of the last menstruation is taken as the starting point of reference.
The development of a new life begins with the moment when the female ovum is fertilized . When the spermatozoon and the ovum merge, a zygote is formed, which starts dividing in 26-30 hours and forms a multicellular embryo, the dimensions of which, as they say, increase by leaps and bounds.
If in the first four days of its existence the embryo has a size of approximately 0.14 mm, then by the sixth day it reaches 0.2 mm, and by the end of the seventh - 0.3 mm.
On day 7-8, the embryo is implanted into the uterine wall.
On the 12th day of development, the size of the embryo is already 2 mm.
Change in embryo size by week of pregnancy
- at the 3rd week of the development of the embryo, that is, at the 5th week of pregnancy, the ectoderm at the site of the future spine of the baby forms a groove. Then its edges are closed and a neural tube is formed - the future dorsal and brain. By the end of this week, the embryo reaches 4 mm;
- In the fourth week, the central nervous system is formed from the neural tube - the dorsal and the brain. The heart makes its first contraction. Appear rudiments of the legs, hands, eyes and internal organs, begins to flow blood through the blood vessels;
- in 5-6 weeks, the head and facial features of the embryo are formed. Its length is of the order of 1 cm
- at week 7 limbs elongate and begin to form lungs. Fully formed heart. The size of the embryo is 1.5 cm;
- at 8 weeks all the vital organs are almost formed. The size of the embryo is about 2 cm;
- at 9 weeks clearly visible ears, nose, eyelids, mouth, eyes. The height of the baby is about 3 cm and it continues to grow rapidly;
- at 10 weeks, that is, at 12 weeks of pregnancy, the structure of the skeleton fully corresponds to the person. The limbs are lengthened. The blood of the child acquires its own group. The size of the embryo, which now turns into fetal status, can reach 7 cm.
The increase in the size of the embryo can be traced according to the table below.