The gestation period, which lasts approximately 9 months, begins with fertilization and ends with birth. It can be divided into three unequal parts – stages of pregnancy:
- The stage of the eggs (pre-germinal)
- The stage of the embryo (embryonic)
- The stage of the fetus (fetal)
However, the most habitual way to count pregnancy terms is month by month or week by week.
Pregnancy Stages by Months & Weeks
|Which Trimester||How Many Months||How Many Weeks|
|FIRST TRIMESTER||1||1,2, 3, 4|
|2||5, 6, 7, 8|
|3||9, 10, 11, 12, 13|
|SECOND TRIMESTER||4||14, 15, 16, 17|
|5||18, 19, 20, 21|
|6||22, 23, 24, 25, 26|
|THIRD TRIMESTER||7||27, 28, 29, 30|
|8||31, 32, 33, 34, 35|
|9||36, 37, 38, 39, 40,41,42|
The three stages of pregnancy
The stage of the eggs (pre-germinal)
This stage lasts from 0 to 2 weeks. Starting with fertilization of an ovum by sperm, and then it is called an egg. The journey of the egg along the tube to the uterus takes 3-4 days. Some more days are required for an egg to find a suitable place and attach to the wall of the uterus.
If a fertilized egg cannot survive in the mucosa, menstrual flow (“tears on a failed pregnancy”) begins at 7-8 day after conception; a woman may not even suspect that she was pregnant and had a miscarriage. If the egg has attached to the wall of a uterus and was fixed there, the development of the future child proceeds. Thus begins the production of the special hormone, which contributes to the delay of menstruation. By this time the egg consists of 120 -200 cells and their division is continuous. From one part of the cell the formation of rudimentary organs and tissues of the future baby starts, from the other part starts the development of the amniotic bubble, placenta, umbilical cord. This stage is the most vulnerable among the stages of pregnancy.
Learn more about First Signs of Pregnancy
The stage of the embryo (embryonic)
This stage covers the period from the 3rd week to the end of the second month of development. During this time there is an anatomic and physiological differentiation of various systems and organs. The embryo floats freely in the created amniotic bubble, and is connected to placenta with the umbilical cord, which contains a vein and two arteries. Through the vein the evolving body receives nutrients and oxygen, and the toxins are discharged through the arteries. The rate of cell division at this stage increases, and they form so-called “germ layers”, which are three. The outer layer forms the skin, hair and mammary glands, cornea of the eye, tooth enamel, as well as nervous system with sensor organs and the respiratory system. The mid layer forms skeleton, muscles, cardiovascular system, blood and blood-forming organ. The internal layer forms the gastrointestinal tract and digestive glands, which are located in the wall of the stomach and intestines, and large organs, such as the liver and pancreas. The development of organs and systems of the embryo is a hard genetic program, which goes in strict sequence.
The stage of the fetus (fetal)
This stage begins with the third month of development and ends with the emergence of signs of patrimonial activity – contractions and childbirth. During this time, the organs and systems of the future child improve, train and develop new functions. On the 3rd month the features of the fetus are fully determined: the fetus has eyelids and well-formed nose and ears. The fetus is already able to grimace. A study found that mimicry of the fetus reflects the changing face of his mother at the time when she laughs or cries. The ossification of the skeleton and the development of the muscular system continues. Hands have grown, so that the fetus can touch the head, and can scratch itself with nails, and also knows how to clench fists. Its length is about 7 inches, and it has enough room in an amniotic bubble. This allows the fetus to freely float, move its feet, head, and train muscles. Mother still does not feel these movements. Genitals are formed, and by the end of the 12-th week the sex of the child may be determined via US.
By the end of the fourth month the fetus length is about 20 cm. On the third week of the fifth month the pregnant woman starts feeling the movements of fetus. However, some pregnant women evidently notice them 10 days earlier. First registration of fetal movements by the mother is an important feature that allows to calculate quite precisely date of the forthcoming childbirth. By the end of the fifth month of pregnancy the formation of cells of the cerebral cortex basically completes. Their loss under influence of any factors is not compensated/ For the rest of life people live with the number of cells that formed in the cerebral cortex during this time. By the 6th month the size of fetus increases by 5-7 cm. By the 7th month all critical systems are sufficiently developed and can support special care to maintain its viability outside the mother’s organism in case of premature birth. By the end of 7th-month fetal weight is 1.5 kg, and the body length is 40 cm. By the 8-th – 9-th month growth rate of the fetus reduces.
Thus, by the fortieth week the weight of the fetus reaches an average of more than 3 kg, and body length more than 50 cm, further growth becomes dangerous for the mother. The last of the stages of pregnancy comes to an end. It’s time!