During pregnancy, rapid growth is necessary to ensure the complete development of a baby within the 40 week gestational period. Pregnancy is broken up into three trimesters, each which feature significant developmental stages for babies.
Conception
Pregnancy begins when an egg is fertilized by a sperm, forming a zygote. Immediately after fertilization, the zygote begins dividing at a very rapid pace, creating the cells which will form the baby, as well as the placenta and membranes which surround the baby. Once the zygote begins dividing, MayoClinic.com notes that it is known as a blastocyst, which implants into the wall of the uterus and begins to grow. Fertilization and implantation occur around two weeks gestation.
First Trimester Development
The first trimester refers to the first 13 gestational weeks of pregnancy. This trimester is filled with extremely rapid growth, beginning with the nervous system which includes the brain and spinal cord. The circulatory system, including the heart, stomach and intestines also form during this time. The placenta which provides nutrition for the baby forms during the first trimester. The American Pregnancy Association notes that the heart begins to beat, arms and legs form, and the baby begins to take shape.
Second Trimester Development
The second trimester refers to gestational weeks 14 through 26. During this time, the baby begins to produce urine, which releases into the amniotic fluid surrounding the baby. MayoClinic.com explains that bone forms during this time period, forming the skull, arms, legs and rib bones, as well as the rest of the skeleton. Muscles begin to form and strengthen, facial features move into place, and fat begins to develop under the skin. Nerves connect which allow the baby to hear. During the second trimester, a woman will begin to feel her baby move. The baby learns to suck, and may suck on his hands.
Third Trimester Development
The third trimester refers to weeks 27 through 40, or until the baby is born. During this time period, the bones become fully formed and the baby opens her eyes. As the lungs continue to form, the baby practices breathing by inhaling amniotic fluid. A protective coating known as vernix begins to thicken on the skin and the baby begins to rapidly gain weight at a rate of a half pound per week, notes MayoClinic.com.
Complications
During fetal development, any deviation from the normal process of cells dividing and multiplying can result in complications in development. Obgyn.net notes that congenital defects such as Down's syndrome and other chromosomal abnormalities can occur. Unfortunately, some abnormalities lead to miscarriage when proper development cannot continue.
