A pregnancy generally lasts for 40 weeks and is calculated from the first day of a woman's last period, says the American Pregnancy Association. Pregnancy is divided into three trimesters, each lasting about 12 to 14 weeks. The pregnancy then progresses through the stages needed to help the baby develop and mature so that he is ready to be born and survive outside his mother's body.
Conception
Conception is the first stage of a pregnancy and occurs when a woman's egg is fertilized by her partner's sperm. Each parent contributes 23 chromosomes as the baby begins to develop. Pregnancy.org says that a baby's gender is determined at conception. Once conception has successfully happened, the fetus implants in the uterine lining of the mother and the cells begin to divide. These cells become both the placenta and parts of the developing baby.
Embryonic
The embryonic stage happens during the first trimester, according to Science Clarified. During this stage, the embryo begins to develop the functions and structures that make up the body. This includes the muscles, blood, nerves and bone cells as well as heart and nervous system development. During this stage, the blood vessels form and begin carrying blood around the body of the unborn baby. Finally, Science Clarified says that during the embryonic stage, the baby's limbs, eyes and ears begin to form and function.
Fetal
The second and third trimesters make up the fetal development stage. This stage is where most of the baby's bodily functions will complete development so that he is ready to be born. According to the American Pregnancy Association, the fetal development stage is when a baby's hair, eyebrows and eyelashes are formed and become visible. The sucking and swallowing reflexes are also present, and a baby practices them by the intake and output of amniotic fluid. Fingerprints and the nails on the fingers and toes also finish developing in the fetal stage. The sweat glands, liver and pancreas are already operating before birth. The fetus finishes gaining weight and developing the fat needed to survive outside the womb. Finally, the baby's lungs complete development and the baby is ready to be born.
