When an egg is fertilized, about three weeks pass before implantation in the uterus. From then on, during the next 35 weeks, the embryo develops into a fetus, which continues to form inside the uterine cavity until the day of birth. The mother begins to perceive its movements from the fifteenth/twelfth week.
First month
At the end of 4 weeks, the fetus experiences the initial phase of organogenesis, that is, the moment when the organs and the nervous system begin to form. The fetus, which measures between 2 and 5 millimeters, already has a heart and stomach, no mouth or eyes, and the limbs are not yet distinguishable. The embryo, linked through the umbilical cord, floats in the amniotic cavity.
Second month
At this stage of pregnancy, the organs are more developed. The fetus does not yet see well and does not feel, is 3 centimeters long and weighs about 3 grams. The brain, liver, stomach and pancreas are fully formed. The limbs, spine and first muscles begin to stretch and the heart begins to develop to the right and left. The nose and ears become visible, and the tongue and optic nerve begin to define themselves.
A pregnancy lasts approximately 40 weeks.
Third month
During the third month the fetus triples in size. Nerve cells develop and the skeleton begins to develop. The fingers can curl into a fist, but the brain does not yet control any movement. The eyes definitely form, the mouth opens, the lips are delineated and slowly the nostrils begin to open.
Sucking instincts also begin to develop and by the end of the month (13th week), the fetus will weigh about 65 grams and measure 12 centimeters.
Fourth month
During the fourth month, the body is covered with lanugo, a fine hair.
The appendix of the intestine is formed and amniotic fluid flows in and out of the lungs, although respiratory function has not yet developed.
The hearing apparatus is defined; the fetus does not yet see, but the retina of the eyes is already sensitive to light.
Fifth month
This month the woman should undergo a morphological ultrasound. The muscles are getting stronger, a slight hairiness begins to be visible on the head and the fingerprints are defined. This is the time for the second ultrasound, called morphological, which often allows us to see the sex of the baby. Fingerprints are defined, a light hair starts to cover the head, the iris of the eye is pigmented. Around the twenty-first week, the fetus weighs about 300 grams and measures about 24 centimeters.
Sixth month
During this month, the sexual organs, dental buds and fingernails are forming. One of the most exciting phases for the mother and father begins, the baby begins to feel and react to touch and sounds.
Seventh month
This is the phase in which nervous and cerebral maturation is complete. The baby can open its eyes and feel light. The baby weighs about 1,500 grams and is about 37 centimeters long.
Eighth month
During the eighth month, hearing is refined, the baby feeds on amniotic fluid, and the sense of taste, digestive tract, kidneys and nails develop. The baby begins to be sensitive to pain.
Ninth month
During the last month of pregnancy, the baby becomes chubbier due to the accumulation of subcutaneous fat. It begins to position itself head down (in 95% of cases), preparing for delivery. However, the brain is not yet fully developed, but continues to develop rapidly.