The main stages of fetal development can be divided into three broad categories, Conception, Embryonic development and finally fetal development:
Conception: Even before the actual conception of formation of the zygote, the body is preparing for the fertilization of the female egg by the male sperm and consequent pregnancy.
So this stage of the pregnancy actually begins a couple of weeks before the actual conception, when the inside of the uterus is prepared by the creation of a nutrient and blood rich lining.
The conception which takes place at two weeks (since the pregnancy is dated by the last period rather than the actual date of conception), is therefore the first stage of the pregnancy and which presupposes healthy and normal hormone levels, healthy egg and sperm, as well as healthy fallopian tubes, ovaries and uterus.
Embryonic Development: This is the next crucial, main stage of fetal development, which comes about when the conception stage is successfully navigated. This is the embryonic stage, which we also commonly know as the first trimester.
The embryo is completely formed by the 5th week of the pregnancy. The central nervous system starts to develop by the third week as also the heart beat.
By the fourth week there is the development of the anterior brain and the arms and legs also begin to form buds out of the body’s trunk. By the eight week, visible male characteristics start to form in the male embryos.
By week 12, the embryo is the size of a large egg, about 3 ½ inches long and the placenta is well developed. Fingers and toes can just be made out at this stage.
Fetal Development: The brain is developed to a large degree when you are 16 weeks pregnant, to the extent that the fetus can make sucking and swallowing motions as well as practice breathing.
Fetal movement is able to be discerned and by 20 weeks, at the half way stage, lanugo (fine hair that covers the fetal body) and vernix, the sticky substance that protects the body from the amniotic fluid also form.
When you are 29 weeks pregnant, the fetus is considered viable; which means that the baby is capable of surviving outside the womb as long as the lungs are mature enough to breathe on their own.
By the 36th week the baby has matured to the extent that it can survive on its own outside the womb and by itself, about 5 ½ pounds at 18 inches in length.