Pregnancy Stages of Fetal Development

Over the past several decades, medical scientists have learned a great deal about what happens during pregnancy. Pregnancy now is divided into three separate stages, called trimesters, based on the discoveries of these professionals. Each of these stages is different in terms of the development of the fetus.

Stage 1

• The first stage (trimester) of pregnancy covers the first 12 weeks of the entire pregnancy. During this time, the fetus starts out as two cells, called gametes, which come together to form a single cell, called a zygote. The zygote quickly divides into more cells, and by the end of the first trimester, the group of cells, called an embryo, typically reaches around three inches in length. The heart can start to beat in as little as three weeks after conception. The head of the embryo is very large compared to the rest of the body, but by the end of the 12th week, the embryo has a clearly visible spine, as well as the beginning of teeth buds, eyes, fingers and toes, and vital organs.

Stage 2

• The second stage (trimester) of pregnancy includes weeks 13 to 25 of the entire pregnancy. By the middle of this trimester, the embryo, now called a fetus, has ears that may be developed enough to hear the voice of the mother. Sleeping patterns of the fetus are distinct, and fetal movement, called quickening, usually is felt for the first time. Bones harden, fine hair (lanugo) forms all over the body of the fetus, and the fetus reaches about 14 inches in length.

Stage 3

• The third and final stage (trimester) of pregnancy includes weeks 26 to birth. During this stage, most of the vital organs have formed, although some, like the brain, still develop right up until delivery. The main task for the fetus during the end of this trimester is to put on weight---the fetus may gain up to half a pound a week during the final weeks. The fetus also gets into position for birth. A typical length reached by the end of this trimester is between 18 to 22 inches.

Prenatal Care and Health

• Because the first trimester is the stage of pregnancy when the baby is most susceptible to birth defects, it is important for a pregnant woman to get good prenatal care as soon as possible after finding out about a conception. If possible, it is recommended that those who may become pregnant prepare for the pregnancy by getting their diet in order and stopping habits like smoking that can cause problems with the baby.

Maternal Diet

• Maternal diet has a large impact on the development of a baby during pregnancy. Folic acid and calcium are two of the most important items a baby needs to develop. Meals should be well-balanced, but mothers-to-be should not diet when they are pregnant. Additionally, mothers-to-be shouldn't eat too much---only 300 to 800 extra calories a day are needed to support a singleton pregnancy. Eating more than this can lead to gestational diabetes and other problems.